CJASN ePress. Published on September 19, 2018 as doi: 10.2215/CJN.03990318 Article

CKD in Patients with Bilateral Oophorectomy

Andrea G. Kattah,1 Carin Y. Smith ,2 Liliana Gazzuola Rocca,3 Brandon R. Grossardt,2 Vesna D. Garovic,1 and Walter A. Rocca3,4

Abstract Background and objectives Premenopausal women who undergo bilateral oophorectomy are at a higher risk of morbidity and mortality. Given the potential benefits of on kidney function, we hypothesized that women who undergo bilateral oophorectomy are at higher risk of CKD. 1Division of Nephrology and Design, setting, participants, & measurements We performed a population-based of 1653 women Hypertension, residing inOlmstedCounty, Minnesota whounderwent bilateral oophorectomy before age 50 years oldand before Department of Internal 2 the onset of menopause from 1988 to 2007. These women were matched by age (61 year) to 1653 referent women Medicine, Divisions who did not undergo oophorectomy. Women were followed over a median of 14 years to assess the of of Biomedical Statistics and fi , 2 . CKD. CKD was primarily de ned using eGFR (eGFR 60 ml/min per 1.73 m on two occasions 90 days apart). Informatics and Hazard ratios were derived using Cox proportional hazards models, and absolute risk increases were derived 3Epidemiology, using Kaplan–Meier curves at 20 years. All analyses were adjusted for 17 chronic conditions present at index date, Department of Health race, education, body mass index, smoking, age, and calendar year. Sciences , and 4Department of Neurology, Mayo Results Women who underwent bilateral oophorectomy had a higher risk of eGFR-based CKD (211 events for Clinic, Rochester, oophorectomy and 131 for referent women; adjusted , 1.42; 95% confidence interval, 1.14 to 1.77; Minnesota absolute risk increase, 6.6%). The risk was higher in women who underwent oophorectomy at age #45 years old (110 events for oophorectomy and 60 for referent women; adjusted hazard ratio, 1.59; 95% confidence interval, 1.15 Correspondence: to 2.19; absolute risk increase, 7.5%). Dr.WalterA.Rocca, Division of # , ConclusionsPremenopausal women who undergo bilateral oophorectomy, particularly those 45 years old, are at Department of Health higher risk of developing CKD, even after adjusting for multiple chronic conditions and other possible Sciences Research, confounders present at index date. Mayo Clinic, 200 First ccc–ccc Street SW, Rochester, Clin J Am Soc Nephrol 13: , 2018. doi: https://doi.org/10.2215/CJN.03990318 MN 55905. Email: [email protected]

Introduction Women who undergo bilateral oophorectomy be- Estrogen has shown protective effects on the kidneys fore natural menopause (often performed concur- in both animal models and observational human rently with hysterectomy) may have a particularly studies. In particular, estrogen reduced glomerulo- high risk of harm from prolonged estrogen depriva- sclerosis and glomerular permeability in ischemia- tion (12). There is increasing evidence that premeno- reperfusion injury in various animal models (1). In one pausal women who undergo bilateral oophorectomy model of sclerosis-prone mice, ovariectomy caused may be at a higher risk for significant morbidity and severe glomerulosclerosis and kidney dysfunction mortality, particularly if they are younger than age 46 that was then corrected by continuous estrogen re- years old at the time of oophorectomy and do not placement (2,3). Younger women have a lower in- receive adequate estrogen therapy (13–16). Studying cidence of ESKD and slower progression of CKD than this population of women who become acutely and men; however, that advantage disappears after men- surgically menopausal offers a unique opportunity to opause (4–6). In addition, women may have a steeper identify the precise onset of estrogen deprivation as increase in risk of cardiovascular and all-cause mor- well as adjust for the comorbidities and other possible tality for a given lower GFR or higher albuminuria confounders that are present at the index date (time of compared with men (7). Observational studies of oophorectomy). estrogen therapy in women have had variable results, The long-term risk of CKD in women undergoing with some studies showing beneficial effects of estro- bilateral oophorectomy has not been explored pre- genonmarkersofkidneydysfunction,suchas viously. In this population-based cohort study, we albuminuria (8,9), and some other studies showing evaluated the long-term risk of developing CKD in potential harm (10,11). These discrepant studies have women who underwent bilateral oophorectomy com- had significant methodologic differences, including pared with age-matched referent women without the ages of the women studied and the methods of oophorectomy after adjusting for potential con- assessing kidney function. founders, including cardiovascular, metabolic, and www.cjasn.org Vol 13 November, 2018 Copyright © 2018 by the American Society of Nephrology 1 2 Clinical Journal of the American Society of Nephrology

other chronic conditions present at the index date. We also identified the women with two or more codes .30 days apart assessed whether age at the time of oophorectomy and the assigned at any time (before or after the index date). The use of estrogen therapy may modify this risk. complete medical records of these women were then re- viewed, and the Kidney : Improving Global Out- comes criteria for CKD stages 1, 2, and 3b–5wereapplied Materials and Methods (24). These criteria required an eGFR,45 ml/min per 1.73 m2 Cohort Definition and Comorbidities at Index Date and/or the presence of markers of kidney damage (pro- fi Women were identi ed as part of the Mayo Clinic Cohort teinuria or abnormal urinary sediment) over a 3-month Study of Oophorectomy and Aging-2 (MOA-2) as de- period. We excluded stage 3a (defined as an eGFR of 45–60 – scribed extensively elsewhere (15 17). All of the data used ml/min per 1.73 m2 in the absence of proteinuria or abnormal for this study were derived from the medical records urinary sediment), because during the pilot phase of the linkage system of the Rochester Epidemiology Project, study, we noted that patients with stage 3a often went – which has been described elsewhere (18 21). All research undiagnosed by providers and therefore, would have been activities were approved by the Mayo Clinic and Olmsted missed by our targeted chart review. The rationale for adding Medical Center Institutional Review Boards. The cohort this secondary definition was that CKD as defined by eGFR study included women who underwent bilateral oophorec- could be evaluated using laboratory values extracted elec- tomy or second unilateral oophorectomy from January 1, tronically alone, whereas review of urine and 1988 to December 31, 2007 and age-matched referent women sediment requires the clinical context for interpretation. from the same population. The oophorectomy had to be Unfortunately, reviewing the medical records of the entire performed before the onset of menopause and before age 50 cohort was not feasible. We wanted to include CKD stages 1 years old. The date of the surgical procedure was considered and 2 in our analysis, because many of the studies the index date, and simple random sampling was used to suggesting a relationship between estrogen and the kidney identify referent women from the same Olmsted County, evaluated proteinuria as an outcome. Minnesota population born in the same year (61 year) who had not undergone bilateral oophorectomy before the index Statistical Analyses date. Referent women did not have to be menopausal at the Each definition of CKD (eGFR and adjudicated diagnos- index date and remained eligible if they underwent bilateral tic codes) was considered separately for the cohort anal- oophorectomy after the index date. yses, and women with CKD onset before the index date Medical comorbidities present at the index date were were excluded from the corresponding outcome analysis fi electronically abstracted using selected International Classi - (only incident outcomes were assessed). Women were cation of (ICD) diagnosis codes (ICD-8 or ICD-9) (22). followed from index date to the date of CKD onset, or Womenneededtohaveatleasttwodiagnosticcodesina they were censored at the earliest of death, time of last visit . given category separated by 30 days to avoid false positive with a Rochester Epidemiology Project provider (lost to diagnoses (17). Medical records were manually reviewed, and follow-up), or end of the study (December 31, 2014). We fi oophorectomy status was con rmed by trained study person- estimated unadjusted and adjusted hazard ratios (HRs) and nel (primarily L.G.R.). In addition, extensive clinical informa- 95% confidence intervals (95% CIs) using Cox proportional tion was manually abstracted from the medical records, hazards models, with age as the timescale. Cumulative including demographic and reproductive characteristics and incidence curves were estimated using the Kaplan–Meier systemic estrogen therapy after the index date. method, and absolute risks were obtained from the Kaplan– Meier curves at 20 years after oophorectomy or index. Assessment of CKD during Follow-Up Differences between the two cohorts were also measured CKD was defined in two different ways—primarily using using the absolute risk increase (ARI) or absolute risk eGFR values and in a secondary analysis, using adjudicated reduction obtained by subtracting the two absolute risks. diagnostic codes. The primary definition required an The Kaplan–Meier estimates and Cox models were eGFR,60 ml/min per 1.73 m2 on at least two occasions adjusted for potential confounders using inverse probabil- .90 days apart (23). Serum creatinine (Cr) measurements were ity weights derived from a logistic regression model obtained from the electronic indexes of the Rochester Epide- including 17 preexisting chronic conditions, years of educa- miology Project and were available from the Mayo Clinic tion (#12, 13–16, or .16), race (white versus nonwhite), body starting in 1994 and from Olmsted Medical Center in 1998, the mass index (BMI; ,30 versus $30 kg/m2), smoking status two major providers of clinical care in Olmsted County, (current or former versus never), and age and calendar year Minnesota. The Chronic Kidney Disease Epidemiology Col- at baseline (continuous) (25). Inverse probability weights laboration equation was used to calculate eGFR from all were calculated overall and separately within each stratum to electronically available, isotope dilution mass spectrometry- maximize the balance of characteristics at index date. calibrated serum Cr levels (23). The onset of CKD was defined Analyses were performed using SAS version 9.4 (SAS In- as the date of the second reduced eGFR measurement (meeting stitute, Inc., Cary, NC), and tests of statistical significance the time gap specified), and CKD was considered incident if were conducted at the two-tailed a-level of 0.05. the onset was on or after the index date. Women without eGFR Additional details on cohort selection, assessment of results available were assumed to not have CKD. kidney function, methods for statistical analyses in strata by age In the secondary definition, a nephrologist (A.G.K.) at index date and use of estrogen therapy, and methods for reviewed and adjudicated the medical records of women sensitivity analyses are reported in Supplemental Material. The who had received diagnostic codes for CKD. We first strata by age reflect the definition of premature or early compiled a list of ICD diagnosis codes for CKD and then menopause (#45 years old). Clin J Am Soc Nephrol 13: ccc–ccc, November, 2018 Oophorectomy and CKD, Kattah et al. 3

Results 10.3–19.1) and 14.4 years in the referent cohort (IQR, 10.4– Characteristics at Index Date 19.3). The characteristics at index date of women without There were 1653 women in the bilateral oophorectomy prevalent CKD are summarized in Table 1. The majority of cohort and 1653 age-matched referent women. The median women in both cohorts were white; however, the percent- length of follow-up was 14.5 years in women who un- age of whites was higher in the bilateral oophorectomy derwent bilateral oophorectomy (interquartile range [IQR], group. Women who underwent bilateral oophorectomy

Table 1. Baseline characteristics of women without prevalent CKD in the Mayo Clinic Cohort Study of Oophorectomy and Aging-2 from Olmsted County, Minnesota

Characteristica Referent, n=1644 Bilateral Oophorectomy, n=1638

Age at oophorectomy, median (IQR) 44 (40–47) 44 (40–47) Age at oophorectomy, yr, n (%) #45 1028 (63) 1024 (63) 46–49 616 (37) 614 (37) Calendar year of oophorectomy, n (%) 1988–1992 317 (19) 317 (19) 1993–1997 404 (25) 406 (25) 1998–2002 549 (33) 546 (33) 2003–2007 374 (23) 369 (23) Race, n (%) White 1561 (95) 1596 (97) Black 29 (2) 18 (1) Asian 49 (3) 18 (1) Other 5 (0.3) 6 (0.4) Years of education, n (%) ,9 31 (2) 8 (0.5) 9–12 443 (27) 517 (32) 13–16 858 (52) 883 (54) .16 277 (17) 227 (14) Unknownb 35 (2) 3 (0.2) Smoking status, n (%) Never 949 (58) 891 (54) Past 377 (23) 388 (24) Current 318 (19) 359 (22) BMI, kg/m2, median (IQR) 25.9 (22.7–30.4) 27.2 (23.3–32.4) BMI, kg/m2, n (%) ,25.0 697 (42) 590 (36) 25.0–29.9 486 (30) 477 (29) $30.0 438 (27) 571 (35) Unknownb 23 (1) 0 (0) Hysterectomy, n (%) No 1482 (90) 24 (1) Before 162 (10) 156 (10) Concurrent with oophorectomy — 1458 (89) Oophorectomy indication, n (%)c No ovarian indication — 968 (59) Benign condition — 670 (41) Concurrent hysterectomy indication, n (%)d Cancer — 11 (0.7) Suspicion of cancer — 308 (19) Bleeding — 823 (50) Pain — 588 (36) Fibroids or polyps — 412 (25) Prolapse — 335 (20) Endometriosis — 200 (12) Other — 225 (14)

IQR, interquartile range; BMI, body mass index; —, not applicable. aWomen with prevalent CKD defined using eGFR were excluded from this table (nine referent women and 15 women who underwent bilateral oophorectomy). bIn the regression models used to derive inverse probability weights, women with unknown education were assigned to the #12-year group, and women with unknown BMIs were assigned to the ,30-kg/m2 group. cThe indication was listed by the gynecologist in the medical record at the time of oophorectomy. Benign conditions include benign tumors, cyst, or endometriosis in either ovary. No ovarian indication includes women without a benign ovarian condition in either ovary. Historically, the terms “prophylactic,”“elective,” or “incidental” oophorectomy were used; however, we avoided these terms. dThe indication was listed by the gynecologist in the medical record at the time of hysterectomy. Each woman may have more than one indication recorded. 4 Clinical Journal of the American Society of Nephrology

had higher BMIs and were less educated. The majority of The median eGFR level before and closest to the index date women had some estrogen therapy after bilateral oopho- was slightly lower in women who underwent bilateral rectomy (n=1494, 90%), whereas only 479 referent women oophorectomy (95.6 ml/min per 1.73 m2;IQR,82.7–105.7) (29%) had estrogen therapy after the index date (Supple- than in referent women (96.9 ml/min per 1.73 m2; IQR, mental Material has more details). 83.9–106.5; P=0.003). There were 15 women in the bilateral oophorectomy cohort and nine women in the referent Comorbidities Present at Index Date cohort with prevalent CKD at the index date (Supplemental There were significant differences in the burden of Figure 1). After the index date, 211 women in the bilateral chronic diseases at index date in the two cohorts. Women oophorectomy cohort and 131 women in the referent cohort who underwent bilateral oophorectomy were more likely developed incident CKD (unadjusted HR, 1.67; 95% CI, to have previous diagnoses of depression, anxiety, sub- 1.35 to 2.07) (Table 2, Figure 2). The HR remained stance abuse disorders, hyperlipidemia, hypertension, di- significant after adjusting for education, race, BMI, smok- abetes mellitus, cardiac arrhythmias, asthma, and chronic ing, age, calendar year, and the presence of 17 chronic obstructive pulmonary disease. Supplemental Figure 1 conditions at index date using inverse probability weights shows the odds ratios and 95% CIs from case-control (adjusted HR, 1.42; 95% CI, 1.14 to 1.77). The absolute risk analyses for the 17 chronic conditions. Because of these of incident CKD 20 years after the index date was 20.2% differences at index date, inverse probability weighting (95% CI, 17.3% to 23.5%) in the bilateral oophorectomy was used in all adjusted analyses of CKD outcomes to cohort and 13.6% (95% CI, 11.2% to 16.4%) in the referent balance the two cohorts with respect to these chronic cohort (ARI, 6.6%). The HR was higher in women who conditions and other potential confounders. As an exam- underwent oophorectomy at age #45 years old (adjusted ple, Supplemental Figure 2 shows the adjustments ob- HR, 1.59; 95% CI, 1.15 to 2.19; ARI, 7.5%) compared with tained in the overall sample and the stratum #45 years old those at age 46–49 years old (adjusted HR, 1.33; 95% CI, at index date (using the eGFR-based definition of CKD; 0.98 to 1.81; ARI, 6.1%). However, the HRs were not other results are not shown). significantly different across the two strata. In women who underwent oophorectomy at age #45 years old, the HR Primary Analyses: CKD Defined Using eGFR was higher in women who did not take estrogen or stopped Figure 1 shows the number of women in each cohort it before their 46th birthday (adjusted HR, 2.07; 95% CI, who developed CKD using the eGFR-based definition. 0.72 to 5.92; ARI, 11.9%) compared with women who

Figure 1. | Incident CKD defined using eGFR values was more common in women who underwent bilateral oophorectomy. Plasma or serum creatinine (Cr) testswere extracted from the Rochester Epidemiology Project electronic indexes (available back to 1994 from the Mayo Clinic and back to 1998 from the Olmsted Medical Center). eGFR was calculated from Cr values using the Chronic Kidney Disease Epidemiology Collaboration equation. CKD was defined as eGFR values ,60 ml/min per 1.73 m2 on two occasions .90 days apart. CKD present at the index date was considered prevalent, and CKD that developed on or after the index date was considered incident. Clin J Am Soc Nephrol 13: ccc–ccc, November, 2018 Oophorectomy and CKD, Kattah et al. 5

Table 2. Associations of oophorectomy with incident CKD defined by eGFR (primary analyses)

Bilateral Oophorectomy Referent Women Unadjusted Models Adjusted Modelsa Chronic Condition N at N of Absolute Risk, N at N of Absolute Risk, Hazard Hazard Ratio and Strata Person-yr Person-yr P Value P Value Risk Events %(95%CI)b Risk Events %(95%CI)b Ratio (95% CI) (95% CI)

Primary analyses Overall 1638 22,723 211 20.2 (17.3 to 23.5) 1644 22,967 131 13.6 (11.2 to 16.4) 1.67 (1.35 to 2.07) ,0.001 1.42 (1.14 to 1.77) 0.002 Age #45 yr 1024 14,439 110 17.6 (14.2 to 21.7) 1028 14,373 60 10.1 (7.6 to 13.4) 1.88 (1.38 to 2.56) ,0.001 1.59 (1.15 to 2.19) ,0.01 ET.45 yrc 638 7795 75 25.0 (19.1 to 32.3) 597 7298 45 12.5 (8.9 to 17.5) 1.58 (1.10 to 2.27) 0.01 1.52 (1.05 to 2.20) 0.03 No ET or #45 yr 177 1613 17 27.0 (13.5 to 49.6) 161 1628 6 15.1 (4.6 to 43.2) 2.87 (1.15 to 7.21) 0.02 2.07 (0.72 to 5.92) 0.18 Age 46–49 yr 614 8283 101 25.4 (20.2 to 31.6) 616 8593 71 19.3 (14.9 to 24.8) 1.50 (1.11 to 2.03) ,0.01 1.33 (0.98 to 1.81) 0.07 ET.49 yrd 440 5622 71 29.0 (22.5 to 36.9) 422 5592 56 25.9 (19.3 to 34.4) 1.30 (0.92 to 1.85) 0.14 1.18 (0.83 to 1.69) 0.36 No ET or #49 yr 152 1408 20 39.5 (21.3 to 65.1) 153 1485 12 25.2 (11.7 to 49.3) 1.73 (0.85 to 3.52) 0.13 1.34 (0.65 to 2.77) 0.43 First set of sensitivity analysese Overall 1230 15,290 124 23.8 (18.0 to 31.0) 1132 14,399 60 13.7 (9.6 to 19.3) 2.02 (1.49 to 2.74) ,0.001 1.61 (1.17 to 2.21) 0.003 Age #45 yr 753 9440 64 21.4 (14.0 to 31.7) 677 8577 26 11.4 (6.5 to 19.9) 2.28 (1.45 to 3.59) ,0.001 1.71 (1.05 to 2.78) 0.03 ET.45 yrc 434 4714 38 40.0 (15.6 to 78.5) 383 4210 19 11.1 (6.3 to 19.2) 1.77 (1.02 to 3.07) 0.04 1.60 (0.90 to 2.83) 0.11 No ET or #45 144 1178 12 12.5 (5.5 to 27.3)f 125 1105 4 6.3 (2.5 to 15.7) 2.85 (0.92 to 8.76) 0.07 1.54 (0.46 to 5.16) 0.49 Age 46–49 yr 477 5850 60 28.4 (19.8 to 39.6) 455 5821 34 17.1 (11.1 to 26.0) 1.79 (1.18 to 2.72) ,0.01 1.51 (0.98 to 2.31) 0.06 ET.49 yrd 330 3789 41 32.8 (21.8 to 47.4) 304 3615 26 11.9 (7.9 to 18.0)f 1.55 (0.95 to 2.53) 0.08 1.36 (0.81 to 2.27) 0.25 No ET or #49 yr 127 1055 10 12.0 (5.9 to 23.4)f 119 1034 5 8.2 (3.7 to 17.8)f 2.01 (0.68 to 5.92) 0.20 1.32 (0.44 to 4.03) 0.62 Second set of sensitivity analysesg Overall 656 9860 68 14.4 (11.1 to 18.8) 888 12,829 55 8.8 (6.5 to 12.0) 1.46 (1.03 to 2.08) 0.03 1.41 (0.99 to 1.99) 0.06 Age #45 yr 420 6452 37 14.1 (10.0 to 19.6) 592 8503 27 7.3 (4.7 to 11.1) 1.63 (1.00 to 2.67) 0.05 1.58 (0.97 to 2.59) 0.07 Age 46–49 yr 236 3407 31 15.5 (10.1 to 23.3) 296 4326 28 12.0 (7.7 to 18.6) 1.30 (0.78 to 2.16) 0.32 1.27 (0.76 to 2.12) 0.36

95% CI, 95% confidence interval; ET, estrogen therapy. aHazard ratios were calculated using Cox proportional hazards models with age as the timescale and adjusted using inverse probability weights derived from a regression model including 17 chronic conditions present at baseline, years of education (unknown, #12, 13–16, or .16), race (white versus nonwhite), body mass index (unknown or ,30 versus $30 kg/m2), cigarette smoking (current or former versus never), age at baseline (continuous), and calendar year at baseline (continuous). These adjustments were performed separately in each stratum to maximize the balance at baseline. None of the interactions by age were significant. bAbsolute cumulative risk at 20 years after bilateral oophorectomy (or index) calculated using the Kaplan–Meier method. The estimates were adjusted using inverse probability weights derived from a logistic regression model including 17 chronic conditions present at baseline,yearsof education(unknown, #12,13–16,or.16), race(whiteversusnonwhite), bodymass index(unknownor ,30versus$30 kg/m2), cigarette smoking (current or former versus never), age at baseline (continuous), and calendar year at baseline (continuous). These adjustments were performed separately in each stratum to maximize the balance at baseline. cWomen who were taking ET on their 46th birthday after bilateral oophorectomy (only oral or transdermal). Women who developed CKD before their 46th birthday, died or were lost to follow-up before their 46th birthday, or had not reached age 46 years old as of December 31, 2014 were not included in the corresponding analysis. Follow-up for these analyses was started at age 46 years old. None of the interactions by ET were significant in the #45-years-old age stratum. dWomen who were taking ET on their 50th birthday after bilateral oophorectomy (only oral or transdermal). Women who developed CKD before their 50th birthday, died or were lost to follow-up before their 50th birthday, or had not reached age 50 years old as of December 31, 2014 were not included in the corresponding analysis. Follow-up for these analyses was started at age 50 years old. None of the interactions by ET were significant in the 46- to 49-years-old age stratum. eExcluding women with oophorectomy or index date before January 1, 1994 and women with no serum creatinine measurements available. fThe absolute risk was reported at 15 years after bilateral oophorectomy (or index) rather than at 20 years, because the follow-up was shorter. gExcluding women with any of the 17 chronic conditions at the index date or with onset of CKD defined by eGFR or adjudicated diagnostic codes before the index date.

received estrogen through their 46th birthday (adjusted bilateral oophorectomy after the index date but before HR, 1.52; 95% CI, 1.05 to 2.20; ARI, 12.5%). However, the age 50 years old (results not shown). HRs were not significantly different across the two strata. A first sensitivity analysis limited to women with an Secondary Analyses: CKD Defined Using Adjudicated index date in the years 1994–2007 (when electronic Cr Diagnostic Codes measurements were available) and excluding 142 women Figure 3 shows the number of women in each cohort who who did not have any serum Cr measurements (19 from the developed CKD defined using the adjudicated diagnostic bilateral oophorectomy cohort and 123 from the referent codes. CKD was present at the index date in 11 women in cohort) yielded even stronger associations (overall adjusted the bilateral oophorectomy cohort and six women in the HR, 1.61; 95% CI, 1.17 to 2.21) (Table 2). In a second referent cohort (Supplemental Figure 1). Incident CKD sensitivity analysis restricted to women without any developed in 61 women who underwent bilateral oopho- chronic conditions at baseline (excluding 997 women rectomy (28 by eGFR and 33 by urine protein) and 43 from the bilateral oophorectomy cohort and 765 women referent women (25 by eGFR, 17 by urine protein, and one from the referent cohort), the HR was significant in the by abnormal urinary sediment; adjusted HR, 1.17; 95% CI, unadjusted model (HR, 1.46; 95% CI, 1.03 to 2.08) but was 0.79 to 1.74) (Table 3, Figure 2). The HR was also not not significant in the adjusted model (HR, 1.41; 95% CI, 0.99 statistically significant in a first sensitivity analysis re- to 1.99; ARI, 5.6%). The results were virtually unchanged stricted to women with no chronic conditions at baseline from the primary analysis in a third sensitivity analysis, (adjusted HR, 1.25; 95% CI, 0.67 to 2.32) (Table 3). Similar which censored 84 referent women who underwent results to the secondary analysis were observed in an 6 Clinical Journal of the American Society of Nephrology

Figure 2. | Higher cumulative incidence of CKD by eGFR-based criteria (upper panels) and adjudicated diagnostic codes (lower panels) in women who underwent bilateral oophorectomy. Cumulative incidence curves estimated using the Kaplan–Meier method and adjusted using inverse probability weights are shown in red for the bilateral oophorectomy cohort and black for the referent cohort. The hazard ratios (HRs) and corresponding 95% confidence intervals were calculated using Cox proportional hazards models with age as the timescale and adjusted using inverse probability weights. Analyses are shown overall (left panels), for women age #45 years old at the index date (center panels), and for women age 46–49 years old at the index date (right panels). additional sensitivity analysis that censored referent our findings were not statistically significant using the women who underwent bilateral oophorectomy after the adjudicated diagnostic codes, likely because of limited index date but before age 50 years old (results not shown). statistical power. Similarly, the statistical power may have The causes of CKD obtained from medical record abstrac- been limited in some of the stratified analyses due to small tion are described in Supplemental Material. numbers of events. Animal models support the hypothesis that estrogen deprivation may have important direct harmful effects on Discussion kidney structure and function. Mesangial cells that are We found that premenopausal women who underwent critical to the pathogenesis of glomerulosclerosis express bilateral oophorectomy before age 50 years old were at both estrogen receptor subtypes (a and b)inmiceand higher risk of developing CKD compared with a cohort of humans (26,27). Estrogen has been found to prevent the age-matched referent women. This population-based study accumulation of extracellular matrix and decrease the offers several advantages over prior efforts to understand synthesis of type 1 and type 4 collagen (26,28,29). Ovari- the association of menopause and estrogen therapy with ectomy caused significant kidney dysfunction, accumula- kidney function, because we identified women who expe- tion of extracellular matrix, and glomerulosclerosis in one rienced an abrupt onset of menopause. This design allowed study of sclerosis-prone mice (2). In addition, glomerulo- us to adjust for chronic conditions present at the time of sclerosis and albuminuria were both prevented by contin- menopause onset that may affect the risk of CKD. We uous estradiol administration in a subsequent study using found consistent elevations and patterns of risk using both the same mouse model (30). definitions of CKD, with a notably higher risk of CKD in Previous studies in women have suggested that women women #45 years old at the time of oophorectomy and have a lower incidence of ESKD and slower progression of women who did not receive estrogen therapy; however, CKD before menopause than men (5,6). This observed sex Clin J Am Soc Nephrol 13: ccc–ccc, November, 2018 Oophorectomy and CKD, Kattah et al. 7

Figure 3. | Incident CKD defined using adjudicated diagnostic codes was more common in women who underwent bilateral oophorectomy. The electronic indexes of the Rochester Epidemiology Project were screened for a list of International Classification of Diseases (ICD) diagnosis codes for CKD (ICD-8 or ICD-9). The medical records for all women with at least twoof these codes separated by .30 dayswere then reviewed by a nephrologist. CKD was defined as an eGFR,45 ml/min per 1.73 m2 or evidence of kidney damage (proteinuria or activeurinary sediment) on at least two occasions .90 days apart. CKD present at the index date was considered prevalent, and CKD that developed on or after the index date was considered incident. aWe excluded CKD stage 3a, because it often went undiagnosed by the care providers. bStructural abnormalities without evidence of kidney dysfunction were not included (e.g., atrophic kidney, medullary sponge kidney, hydronephrosis, and partial or complete nephrectomy).

difference is often attributed to the beneficial effects of One challenge in studying the effects of estrogen estrogen on the kidney, because the sex difference attenuates therapy in humans is that the age of a woman and the after menopause. A post hoc analysis in the Modification of time since menopause are important factors (timing Diet and Renal Disease Study showed a slower decrease in hypothesis). For example, although the Women’sHealth GFR in women than in men with CKD, particularly in Initiative clinical trials showed an overall higher risk of women younger than age 52 years old (6). However, the coronary heart disease with estrogen therapy (36), a post effect of sex was attenuated after the investigators adjusted hoc analysis showed a trend toward reduced cardiovas- the analyses for BP, proteinuria, and HDL. Therefore, the cular events in women who initiated hormone therapy difference in progression may have been mediated by these closer to the time of menopause compared with those intervening conditions rather than it being due to a direct who initiated hormone therapy later (37). Similarly, a effect of estrogen on kidney function. large Canadian study showed that hormone therapy in At least three observational studies in women and a older women (age .66 years old) was associated with a recent meta-analysis have suggested that estrogen therapy greater rate of decline in eGFR compared with in non- may be associated with a lower risk of albuminuria users (10). By contrast, we observed a higher risk of CKD (8,9,31,32). Estrogen can stimulate the release of nitric after bilateral oophorectomy after adjusting for relevant oxide and cause vasodilation (33,34). Impaired vasodila- comorbid conditions in our cohort of younger women. tion and endothelial dysfunction are seen in CKD, and Our findings suggest that there may be a direct beneficial there is mounting evidence that nitric oxide deficiency may effect of estrogen on kidney function. This is further be linked to acceleration of kidney damage (35). Loss of supported by our observation that women younger than estrogen after bilateral oophorectomy may, therefore, age 46 years old at the time of oophorectomy and who did affect kidney structure and function in several ways, not take estrogen or stopped it before their 46th birthday and it may increase the risk of developing CKD. had a higher HR. 8 Clinical Journal of the American Society of Nephrology

Table 3. Associations of oophorectomy with incident CKD defined by adjudicated diagnostic codes (secondary analyses)

Bilateral Oophorectomy Referent Women Unadjusted Models Adjusted Modelsa Chronic Condition N at Person- N of Absolute Risk, N at Person- N of Absolute Risk, Hazard Ratio Hazard Ratio and Strata P Value P Value Risk yr Events %(95%CI)b Risk yr Events % (95% CI)b (95% CI) (95% CI)

Secondary analyses Overall 1642 23,467 61 5.3 (3.8 to 7.3) 1647 23,530 43 4.7 (3.3 to 6.6) 1.44 (0.98 to 2.12) 0.06 1.17 (0.79 to 1.74) 0.44 Age #45 yr 1024 14,754 39 5.8 (3.9 to 8.6) 1028 14,542 26 4.4 (2.8 to 6.9) 1.50 (0.92 to 2.44) 0.10 1.20 (0.73 to 1.99) 0.48 ET.45 yrc 644 8086 22 5.8 (3.3 to 9.8) 600 7459 19 7.8 (4.6 to 13.3) 1.07 (0.58 to 1.97) 0.84 0.97 (0.52 to 1.81) 0.92 No ET or #45 176 1639 9 25.1 (10.7 to 52.3) 161 1644 2 3.4 (0.9 to 12.2) 4.70 (0.99 to 22.31) 0.05 2.08 (0.39 to 11.10) 0.39 Age 46–49 yr 618 8713 22 4.7 (2.8 to 7.7) 619 8988 17 5.2 (3.0 to 8.9) 1.34 (0.71 to 2.53) 0.36 1.23 (0.64 to 2.35) 0.54 ET.49 yrd 446 5959 14 5.4 (2.7 to 10.5) 425 5855 14 4.1 (2.3 to 7.1) 1.00 (0.47 to 2.10) 0.99 0.83 (0.39 to 1.78) 0.63 No ET or #49 yr 155 1489 5 2.6 (0.9 to 7.2) 154 1599 3 4.4 (0.7 to 24.5) 1.80 (0.46 to 6.99) 0.40 1.20 (0.30 to 4.74) 0.80 Sensitivity analysese Overall 656 10,113 22 4.2 (2.5 to 6.9) 888 13,004 19 3.7 (2.3 to 6.1) 1.37 (0.74 to 2.56) 0.31 1.25 (0.67 to 2.32) 0.48 Age #45 yr 420 6565 14 4.5 (2.4 to 8.5) 592 8572 11 2.7 (1.4 to 5.2) 1.50 (0.68 to 3.30) 0.31 1.32 (0.60 to 2.94) 0.49 Age 46–49 yr 236 3548 8 3.6 (1.6 to 7.9) 296 4432 8 6.0 (2.9 to 12.5) 1.15 (0.42 to 3.14) 0.78 1.11 (0.41 to 3.03) 0.84

95% CI, 95% confidence interval; ET, estrogen therapy. aHazard ratios were calculated using Cox proportional hazards models with age as the timescale and adjusted using inverse probability weights derived from a regression model including 17 chronic conditions present at baseline, years of education (unknown, #12, 13–16, or .16), race (white versus nonwhite), body mass index (unknown or ,30 versus $30 kg/m2), cigarette smoking (current or former versus never), age at baseline (continuous), and calendar year at baseline (continuous). These adjustments were performed separately in each stratum to maximize the balance at baseline. None of the interactions by age were significant. bAbsolute cumulative risk at 20 years after bilateral oophorectomy (or index) calculated using the Kaplan–Meier method. The estimates were adjusted using inverse probability weights derived from a logistic regression model including 17 chronic conditions present at baseline,yearsofeducation(unknown,#12,13–16,or.16), race(whiteversus nonwhite),bodymassindex(unknown or,30 versus$30 kg/m2), cigarette smoking (current or former versus never), age at baseline (continuous), and calendar year at baseline (continuous). These adjustments were performed separately in each stratum to maximize the balance at baseline. cWomen who were taking ET on their 46th birthday after bilateral oophorectomy (only oral or transdermal). Women who developed CKD before their 46th birthday, died or were lost to follow-up before their 46th birthday, or had not reached age 46 years old as of December 31, 2014 were not included in the corresponding analysis. Follow-up for these analyses was started at age 46 years old. None of the interactions by ET were significant in the #45-years-old age stratum. dWomen who were taking ET on their 50th birthday after bilateral oophorectomy (only oral or transdermal). Women who developed CKD before their 50th birthday, died or were lost to follow-up before their 50th birthday, or had not reached age 50 years old as of December 31, 2014 were not included in the corresponding analysis. Follow-up for these analyses was started at age 50 years old. None of the interactions by ET were significant in the 46- to 49-years-old age stratum. eExcluding women with any of the 17 chronic conditions at index date or with onset of CKD defined by eGFR or adjudicated diagnostic codes before the index date.

Observational evidence continues to mount suggesting as therapy may vary by composition, dose, and route of that women who undergo bilateral oophorectomy at a administration. younger age, particularly those without adequate estrogen Our study has some limitations. First, our study focused therapy, have a higher risk of long-term morbidity and on a single geographically defined United States popula- mortality (13,38,39). Findings from the MOA-2 have re- tion, and the observed associations may differ in other cently shown a significant accumulation of multimorbidity populations in the United States and worldwide. Second, after bilateral oophorectomy that may be in part ameliorated we were only able to access serum Cr and urine protein by estrogen therapy (15,16). Levine et al. (40) showed that measurements that were taken as part of routine clinical bilateral oophorectomy may be associated with accelerated care; therefore, some women did not have any measure- aging as measured by the DNA methylation level in blood ments. Women who underwent bilateral oophorectomy and saliva, a biologic marker considered an “epigenetic had more frequent Cr tests and medical visits than referent clock.” These findings have prompted the suggestion that women after the index date. These differences were small in women who become prematurely menopausal after bilateral absolute terms, but they were statistically significant oophorectomy should be treated with hormone therapy at (because of the large sample size) (Supplemental Material). “replacement” doses of estrogen to protect cardiovascular, In our adjudication of diagnostic codes, we found that 85% bone, and neurologic health and slow the pace of aging as of the women with incident CKD had urine protein and Cr opposed to the lowest possible dose to control symptoms values at baseline to confirm absence of CKD; however, the (41). Our study suggests that the kidney may be an additional absence of CKD at baseline could not be confirmed for the organ that can suffer from premature estrogen deprivation. remaining 15% of the women. We tried to define CKD The kidney damage may be due to a combination of direct using two sets of criteria, a more inclusive set of criteria on effects of estrogen deprivation and secondary damage the basis of eGFR alone and a set of criteria on the basis of mediated by the accumulation of multimorbidity in other targeted chart review using diagnostic codes. We organs and systems (e.g., kidney damage secondary to observed a similar pattern of risk in the predefined age hypertension or diabetes). It remains unknown whether and estrogen therapy strata using the two definitions. the effects of exogenous estrogen are similar to the effects of In conclusion, women who undergo bilateral oophorec- endogenous estrogen. In addition, exogenous estrogen used tomy before natural menopause are at higher risk of CKD, Clin J Am Soc Nephrol 13: ccc–ccc, November, 2018 Oophorectomy and CKD, Kattah et al. 9

as defined by reduced eGFR, after adjustments for potential estrogen therapy in postmenopausal women is associated with confounding comorbidities. Therefore, women considering loss of kidney function. Kidney Int 74: 370–376, 2008 bilateral oophorectomy for the prevention of ovarian 11. Monster TB, Janssen WM, de Jong PE, de Jong-van den Berg LT; # Prevention of Renal and Vascular End Stage Disease Study Group: cancer, particularly those at ages 45 years old, need to Oral contraceptive use and hormone replacement therapy are be counseled regarding the potential risks of multimorbid- associated with microalbuminuria. Arch Intern Med 161: 2000– ity, which may include the risk of CKD. There is a trend 2005, 2001 toward conserving the ovaries at the time of hysterectomy 12. JacobyVL,Vittinghoff E, NakagawaS,Jackson R,RichterHE,Chan J, Kuppermann M: Factors associated with undergoing bilateral unless there is a compelling indication to remove them; – salpingo-oophorectomy at the time of hysterectomy for benign however, the practice continues (42 44). Adequate hor- conditions. Obstet Gynecol 113: 1259–1267, 2009 mone therapy in this group of women is essential, but there 13. Rocca WA, Grossardt BR, de Andrade M, Malkasian GD, Melton are limited data regarding the correct dose and route of LJ 3rd: Survival patterns after oophorectomy in premenopausal administration (41). In addition, although estrogen has women: A population-based cohort study. Lancet Oncol 7: 821– fi 828, 2006 been shown to have multiple bene cial effects on the 14. Rivera CM, Grossardt BR, Rhodes DJ, Brown RD Jr., Roger VL, kidney in animal models, human studies have had con- Melton LJ 3rd, Rocca WA: Increased cardiovascular mortality tradictory results. To resolve these contradictions, future after early bilateral oophorectomy. Menopause 16: 15–23, 2009 studies of the effects of hormone therapy on kidney 15. Rocca WA, Gazzuola-Rocca L, Smith CY, Grossardt BR, Faubion function should be guided by the timing hypothesis (i.e., SS, Shuster LT, Kirkland JL, Stewart EA, Miller VM: Accelerated accumulation of multimorbidity after bilateral oophorectomy: A the effects of estrogen vary with the age of women). population-based cohort study. Mayo Clin Proc 91: 1577–1589, 2016 Acknowledgments 16. Rocca WA, Gazzuola Rocca L, Smith CY, Grossardt BR, Faubion This study used the resources of the Rochester Epidemiology SS, Shuster LT, Kirkland JL, Stewart EA, Miller VM: Bilateral oo- Project, which is supported by National Institute on Aging, National phorectomy and accelerated aging: Cause or effect? J Gerontol A Biol Sci Med Sci 72: 1213–1217, 2017 Institutes of Health (NIH) awards R01 AG034676 and R01 17. Rocca WA, Gazzuola Rocca L, Smith CY, Grossardt BR, Faubion AG052425. This study was also supported by funds from the Mayo SS, Shuster LT, Stewart EA, Mielke MM, Kantarci K, Miller VM: Clinic Research Committee (W.A.R.). W.A.R. was partly supported Cohort profile: The Mayo Clinic Cohort Study of Oophorectomy by NIH grants P50 AG044170, U01 AG006786, and P01 AG004875. and Aging-2 (MOA-2) in Olmsted County, Minnesota (USA). BMJ The content of this article is solely the responsibility of the authors Open 7: e018861, 2017 fi 18. St Sauver JL, Grossardt BR, Yawn BP, Melton LJ 3rd, Rocca WA: and does not necessarily represent the of cial views of the NIH. Use of a medical records linkage system to enumerate a dynamic population over time: The Rochester Epidemiology Project. Am J Disclosures Epidemiol 173: 1059–1068, 2011 None. 19. St Sauver JL, Grossardt BR, Leibson CL, Yawn BP, Melton LJ 3rd, Rocca WA: Generalizability of epidemiological findings and public health decisions: An illustration from the Rochester Epi- References demiology Project. Mayo Clin Proc 87: 151–160, 2012 1. Hutchens MP, Fujiyoshi T, Komers R, Herson PS, Anderson S: 20. Rocca WA, Yawn BP, St Sauver JL, Grossardt BR, Melton LJ 3rd: Estrogen protects renal endothelial barrier function from History of the Rochester Epidemiology Project: Half a century of ischemia-reperfusion in vitro and . Am J Physiol Renal medical records linkage in a US population. Mayo Clin Proc 87: Physiol 303: F377–F385, 2012 1202–1213, 2012 2. Elliot SJ, Karl M, Berho M, Potier M, Zheng F, Leclercq B, Striker 21. St Sauver JL, Grossardt BR, Yawn BP, Melton LJ 3rd, Pankratz JJ, GE, Striker LJ: Estrogen deficiency accelerates progression of Brue SM, Rocca WA: Data resource profile: The Rochester Epi- glomerulosclerosis in susceptible mice. Am J Pathol 162: 1441– demiology Project (REP) medical records-linkage system. Int J 1448, 2003 Epidemiol 41: 1614–1624, 2012 3. Karl M, Berho M, Pignac-Kobinger J, Striker GE, Elliot SJ: Differ- 22. Goodman RA, Posner SF, Huang ES, Parekh AK, Koh HK: Defining ential effects of continuous and intermittent 17beta-estradiol and measuring chronic conditions: Imperatives for research, replacement and tamoxifen therapy on the prevention of glo- policy, program, and practice. Prev Chronic Dis 10: E66, 2013 merulosclerosis: Modulation of the mesangial phenotype in 23. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF 3rd, vivo. Am J Pathol 169: 351–361, 2006 Feldman HI, Kusek JW, Eggers P, Van Lente F, Greene T, Coresh J; 4. Silbiger S, Neugarten J: Gender and human chronic renal disease. CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration): Gend Med 5[Suppl A]: S3–S10, 2008 A new equation to estimate glomerular filtration rate. Ann Intern 5. Kummer S, von Gersdorff G, Kemper MJ, Oh J: The influence of Med 150: 604–612, 2009 gender and sexual hormones on incidence and outcome of 24. Stevens PE, Levin A; Kidney Disease: Improving Global Out- chronic kidney disease. Pediatr Nephrol 27: 1213–1219, 2012 comes Chronic Kidney Disease Guideline Development Work 6. Coggins CH, Breyer Lewis J, Caggiula AW, Castaldo LS, Klahr S, Group Members: Evaluation and management of chronic kidney Wang SR: Differences between women and men with chronic disease: Synopsis of the kidney disease: Improving global out- renal disease. Nephrol Dial Transplant 13: 1430–1437, 1998 comes 2012 clinical practice guideline. Ann Intern Med 158: 7. NitschD, Grams M, Sang Y,BlackC, Cirillo M, Djurdjev O, Iseki K, 825–830, 2013 Jassal SK, Kimm H, Kronenberg F, Oien CM, Levey AS, Levin A, 25. Harder VS, Stuart EA, Anthony JC: Propensity score techniques Woodward M, Hemmelgarn BR; Chronic Kidney Disease Prog- and the assessment of measured covariate balance to test causal nosis Consortium: Associations of estimated glomerular filtration associations in psychological research. Psychol Methods 15: rate and albuminuria with mortality and renal failure by sex: A 234–249, 2010 meta-analysis. BMJ 346: f324, 2013 26. Potier M, Karl M, Zheng F,Elliot SJ, Striker GE, Striker LJ: Estrogen- 8. Schopick EL, Fisher ND, Lin J, Forman JP, Curhan GC: Post- related abnormalities in glomerulosclerosis-prone mice: Re- menopausal hormone use and albuminuria. Nephrol Dial duced mesangial cell estrogen receptor expression and pro- Transplant 24: 3739–3744, 2009 sclerotic response to . Am J Pathol 160: 1877–1885, 9. Agarwal M, Selvan V, Freedman BI, Liu Y, Wagenknecht LE: The 2002 relationship between albuminuria and hormone therapy in 27. Potier M, Elliot SJ, Tack I, Lenz O, Striker GE, Striker LJ, Karl M: postmenopausal women. Am J Kidney Dis 45: 1019–1025, 2005 Expression and regulation of estrogen receptors in mesangial 10. Ahmed SB, Culleton BF, Tonelli M, Klarenbach SW, Macrae JM, cells: Influence on matrix metalloproteinase-9. J Am Soc Nephrol Zhang J, Hemmelgarn BR; Alberta Kidney Disease Network: Oral 12: 241–251, 2001 10 Clinical Journal of the American Society of Nephrology

28. Silbiger S, Lei J, Neugarten J: Estradiol suppresses type I collagen 38. Parker WH, Broder MS, Chang E, Feskanich D, Farquhar C, Liu Z, synthesis in mesangial cells via activation of activator protein-1. Shoupe D, Berek JS, Hankinson S, Manson JE: Ovarian conser- Kidney Int 55: 1268–1276, 1999 vation at the time of hysterectomy and long-term health outcomes 29. Silbiger S, Lei J, Ziyadeh FN, Neugarten J: Estradiol reverses TGF- in the Nurses’ Health Study. Obstet Gynecol 113: 1027–1037, beta1-stimulated type IV collagen gene in murine 2009 mesangial cells. Am J Physiol 274: F1113–F1118, 1998 39. Parker WH, Feskanich D, Broder MS, Chang E, Shoupe D, 30. Catanuto P, Doublier S, Lupia E, Fornoni A, Berho M, Karl M, Farquhar CM, Berek JS, Manson JE: Long-term mortality associ- Striker GE, Xia X, Elliot S: 17 Beta-estradiol and tamoxifen up- ated with oophorectomy compared with ovarian conservation regulate estrogen receptor beta expression and control podocyte in the Nurses’ Health Study. Obstet Gynecol 121: 709–716, signaling pathways in a model of type 2 diabetes. Kidney Int 75: 2013 1194–1201, 2009 40. Levine ME, Lu AT, Chen BH, Hernandez DG, Singleton AB, 31. Fung MM, Poddar S, Bettencourt R, Jassal SK, Barrett-Connor E: A Ferrucci L, Bandinelli S, Salfati E, Manson JE, Quach A, Kusters cross-sectional and 10-year prospective study of postmenopausal CD, Kuh D,Wong A, Teschendorff AE, WidschwendterM, Ritz BR, estrogen therapyand blood pressure, renal function, and albuminuria: Absher D, Assimes TL, Horvath S: Menopause accelerates bi- TheRanchoBernardoStudy.Menopause 18: 629–637, 2011 ological aging. Proc Natl Acad Sci U S A 113: 9327–9332, 2016 32. Kattah AG, Suarez MLG, Milic N, Kantarci K, Zeydan B, Mosley T, 41. Faubion SS, Files JA, Rocca WA: When lowest dose for shortest Turner ST, Ware EB, Kardia SLR, Garovic VD: Hormone therapy amount of time does not apply. J Womens Health (Larchmt) 25: and urine protein excretion: A multiracial cohort study,systematic 416–417, 2016 review, and meta-analysis. Menopause 25: 625–634, 2018 42. Evans EC, Matteson KA, Orejuela FJ, Alperin M, Balk EM, El- 33. Guetta V, Quyyumi AA, Prasad A, Panza JA, Waclawiw M, Nashar S, Gleason JL, Grimes C, Jeppson P, Mathews C, Wheeler Cannon RO 3rd: The role of nitric oxide in coronary vascular TL, Murphy M; Society of Gynecologic Surgeons Systematic effects of estrogen in postmenopausal women. Circulation 96: Review Group: Salpingo-oophorectomy at the time of benign 2795–2801, 1997 hysterectomy: A . Obstet Gynecol 128: 476– 34. ChenZ,YuhannaIS,Galcheva-GargovaZ,KarasRH,Mendelsohn 485, 2016 ME, Shaul PW: Estrogen receptor alpha mediates the nongenomic 43. Rocca WA, Faubion SS, Stewart EA, Miller VM: Salpingo- activation of endothelial nitric oxide synthase by estrogen. J Clin oophorectomy at the time of benign hysterectomy: A systematic Invest 103: 401–406, 1999 review. Obstet Gynecol 129: 202–203, 2017 35. Baylis C: Nitric oxide deficiency in chronic kidney disease. Am J 44. Mahal AS, Rhoads KF, Elliott CS, Sokol ER: Inappropriate oo- Physiol Renal Physiol 294: F1–F9, 2008 phorectomy at time of benign premenopausal hysterectomy. 36. Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg Menopause 24: 947–953, 2017 C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC, Kotchen JM, Ockene J;WritingGroup for theWomen’s Health Received: March 28, 2018 Accepted: August 20, 2018 Initiative Investigators: Risks and benefits of estrogen plus pro- gestin in healthy postmenopausal women: Principal results From the Women’s Health Initiative randomized controlled trial. JAMA Published online ahead of print. Publication date available at 288: 321–333, 2002 www.cjasn.org. 37. Rossouw JE, Prentice RL, Manson JE, WuL,Barad D, BarnabeiVM, Ko M, LaCroix AZ, Margolis KL, Stefanick ML: Postmenopausal This article contains supplemental material online at http://cjasn. hormone therapy and risk of cardiovascular disease by age and asnjournals.org/lookup/suppl/doi:10.2215/CJN.03990318/-/ years since menopause. JAMA 297: 1465–1477, 2007 DCSupplemental. Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

Supplementary Material

Materials and Methods

Cohort Selection and Medical Comorbidities

The Mayo Clinic Cohort Study of Oophorectomy and Aging-2 (MOA-2) is a population-

based cohort study of Olmsted County, MN women. The data were collected using the medical

records-linkage system of the Rochester Epidemiology Project as reported in detail elsewhere.(1-

3) Bilateral oophorectomy was identified by screening the electronic indexes of the Rochester

Epidemiology Project for procedure codes for oophorectomy from the International

Classification of Diseases, 9th Edition (ICD-9) from January 1, 1988 through December 31,

2007, as previously described.(4, 5) Women who underwent bilateral oophorectomy due to

ovarian or other estrogen-sensitive malignancies or due to a high risk of ovarian cancer were

excluded.

Assessment of Kidney Function to Apply the Diagnosis of Chronic Kidney Disease (CKD)

Serum creatinine (Cr) and protein measurements were reviewed prior to the index date or

>30 days after the index date, to exclude the immediate effects of surgery. Estimated glomerular filtration rate (eGFR) was calculated from IDMS calibrated serum creatinine measurements using the CKD-EPI equation.(6) Both inpatient and outpatient creatinine tests were included.

Dipstick measurements of proteinuria were not included. Spot urine protein-to-Cr ratios, protein-to-osmolarity ratios, albumin-to-Cr ratios, and 24-hour urine collections for albumin and total protein excretion were all acceptable measurements (protein-to-osmolarity ratios are routinely reported by the Mayo Clinic laboratory on all spot urine measurements).(7) However, spot urine measurements that were contaminated by non-glomerular hematuria or by an active

1

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

urinary tract infection were excluded. Abnormal urinary sediment was defined as presence of

casts or dysmorphic hematuria. Women with reduced eGFR levels or markers of kidney damage

due to separate episodes of acute kidney injury were not considered to have CKD. Women with

structural abnormalities of the kidney identified by imaging, but with normal eGFR and no

markers of kidney damage, were not considered to have CKD. This exclusion criterion was used

to reduce the possible surveillance bias caused by the higher frequency of abdominal imaging in

the oophorectomy group. The onset of CKD was the date of the second qualifying eGFR,

abnormal protein measurement, or abnormal urinary sediment (meeting the time gap specified),

and CKD was considered incident if onset was on or after the index date.

Statistical Methods – Stratified Analyses and Sensitivity Analyses

Analyses were performed overall and in strata by age at index date (≤45 vs. 46-49 years),

and by use of estrogen therapy following the oophorectomy (within age strata; use to the 46th birthday vs. not; or use to the 50th birthday vs. not). Robust sandwich covariance estimates were

used to account for women who were included in both cohorts (e.g., referent women who

subsequently underwent bilateral oophorectomy). The proportional hazards assumption was

assessed using graphical methods and the addition of time-dependent coefficients to the Cox

models. None of the models violated this assumption.

We performed three sets of sensitivity analyses to 1) exclude women who did not have

any serum Cr measurements in their records and women with an index date before 1994 (only for

the eGFR-based definition of CKD), 2) to exclude women with any of the 17 chronic conditions

or with onset of CKD by either definition prior to index date, and 3) to censor referent women at

the date of subsequent bilateral oophorectomy if performed before age 50 years. The first

sensitivity analysis was performed to account for missing Cr data either due to lack of routine 2

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

testing for a given woman or due to the date ranges of electronically available data. The second

and third sets of sensitivity analyses were determined a priori.

Results

Menopausal Status and Estrogen Therapy

Among the 1,653 women who underwent oophorectomy, 157 (10%) had hysterectomy

prior to bilateral oophorectomy. Among the 1,653 referent women, 270 (16%) were menopausal

at index date (166 surgical due to hysterectomy, 98 natural, and 6 due to radiation or

chemotherapy). An additional 944 (57%) referent women became menopausal during follow-up

(764 natural, 104 surgical due to bilateral oophorectomy, 67 surgical due to hysterectomy or

thermal ablation, and 9 due to radiation or chemotherapy).

The majority of women received some estrogen therapy after bilateral oophorectomy

(n=1,494, 90%), whereas only 479 referent women (29%) had estrogen therapy after the index

date. Oral estrogen was most commonly used, either alone or in combination with patch usage.

A total of 1,265/1,494 (85%) women who underwent oophorectomy and 409/479 (85.4%)

referent women took oral estrogen after index. The median (IQR) cumulative years of estrogen

therapy after index was 7.1 (4.0-11.0) in the bilateral oophorectomy cohort and 4.9 (IQR 2.5-8.4)

in the referent cohort. Among women who were ≤45 years of age at oophorectomy (n=1,031),

63% were on estrogen therapy on their 46th birthday. Among women who were 46-49 years at

the time of oophorectomy (n=622), 72% were on estrogen therapy on their 50th birthday.

Exploration of Potential Surveillance Bias

The number of Cr tests and contacts with the healthcare system (visits) were obtained for each woman, excluding any visits or tests performed after the onset of CKD, and excluding a ±1

3

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

year time window around oophorectomy (or index date). The density of Cr tests and visits were

calculated for each woman as the number of events divided by the corresponding length of

medical record. Although both densities were similar in the oophorectomy and referent cohorts,

the differences were statistically significant (because of the large sample size). Before index, the

median density of Cr tests was 0 per year for both groups (oophorectomy IQR 0-0.11; referent

IQR 0-0.07; P<0.001), whereas the median visit density was 1.9 per year (IQR 1.1-4.0) for the

oophorectomy group and 1.6 (IQR 1.0-3.2; P<0.001) for the referent group. After index, the

median density of Cr tests was 0.58 per year (IQR 0.23-1.13) for the oophorectomy group and

0.38 (IQR 0.11-0.83; P<0.001) for the referent group, whereas the median visit density was 8.4

per year (IQR 5.2-14.2) for the oophorectomy group and 6.4 (IQR 3.8-10.4; P<0.001) for the

referent group.

Causes of CKD from Medical Records

A total of 77 women who underwent bilateral oophorectomy and 54 referent women had

a diagnosis of prevalent or incident CKD in their medical records. The most common cause

listed in the records was diabetes mellitus (30 women who underwent bilateral oophorectomy, 21

referent women). CKD was attributed to medications, such as non-steroidal anti-inflammatory drugs or antibiotics, in 16 women who underwent bilateral oophorectomy and in 6 referent women. Kidney biopsies were performed in 6 women who underwent bilateral oophorectomy and in 2 referent women; 7 of 8 biopsies showed glomerular diseases. Six women who underwent bilateral oophorectomy and 2 referent women also developed end-stage renal disease.

4

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

References

1. St Sauver JL, Grossardt BR, Yawn BP, Melton LJ, 3rd, Rocca WA. Use of a medical records linkage system to enumerate a dynamic population over time: the Rochester epidemiology project. Am J Epidemiol. 2011;173(9):1059-68.

2. Rocca WA, Yawn BP, St Sauver JL, Grossardt BR, Melton LJ, 3rd. History of the

Rochester Epidemiology Project: half a century of medical records linkage in a US population.

Mayo Clin Proc. 2012;87(12):1202-13.

3. St Sauver JL, Grossardt BR, Yawn BP, Melton LJ, 3rd, Pankratz JJ, Brue SM, et al. Data resource profile: the Rochester Epidemiology Project (REP) medical records-linkage system. Int

J Epidemiol. 2012;41(6):1614-24.

4. Rocca WA, Gazzuola-Rocca L, Smith CY, Grossardt BR, Faubion SS, Shuster LT, et al.

Accelerated Accumulation of Multimorbidity After Bilateral Oophorectomy: A Population-

Based Cohort Study. Mayo Clin Proc. 2016.

5. Rocca WA, Gazzuola Rocca L, Smith CY, Grossardt BR, Faubion SS, Shuster LT, et al.

Cohort profile: the Mayo Clinic Cohort Study of Oophorectomy and Aging-2 (MOA-2) in

Olmsted County, Minnesota (USA). BMJ Open. 2017;7(11):e018861.

6. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF, 3rd, Feldman HI, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604-12.

7. Wilson DM, Anderson RL. Protein-osmolality ratio for the quantitative assessment of proteinuria from a random urinalysis sample. Am J Clin Pathol. 1993;100(4):419-24.

5

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

Prevalent Chronic Conditions

Depression

Anxiety

Substance abuse disorders

Dementia

Schizophrenia

Hyperlipidemia

Hypertension

Diabetes

Cardiac arrhythmias

Coronary artery disease

Stroke

Congestive heart failure

Arthritis

Cancer (all types)

Asthma

Chronic obstructive pulmonary disease

Osteoporosis

Prevalent Chronic Kidney Disease

eGFR-based definition

Adjudicated diagnostic code definition

0.050.1 0.25 0.5 1.0 2 4 6 10 15 25

Reduced odds Increased odds Odds Ratios

Supplementary Figure 1. Case-control analysis of the chronic conditions present at index date.

The odds ratios, confidence intervals, and p-values were calculated using conditional logistic regression models (matched pairs). Analyses are presented overall (black diamond) and in strata by age at oophorectomy (red circles for age ≤45 years and blue squares age 46-49 years). Each one of the 17 chronic conditions was defined as having two diagnostic codes separated by more than 30 days prior to the oophorectomy or index date. Estimated glomerular filtration rate (eGFR)-based chronic kidney disease (CKD) was defined as having 2 or more eGFR values <60 ml/min/1.73 m2 6

Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

(calculated from serum creatinine using the CKD-EPI equation) separated by more than 90 days and prior to the oophorectomy or index date. CKD by adjudication of diagnostic codes was defined as having 2 or more eGFR measurements <45 ml/min/1.73 m2 separated by more than 90 days and prior to the oophorectomy or index date, or as having evidence of kidney damage (proteinuria or active urinary sediment) on at least 2 occasions >90 days apart prior to the oophorectomy or index date.

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Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material.

Overall Age ≤45 years Condition or characteristica Condition or characteristica Depression Depression COPD COPD Hypertension Anxiety BMI ≥30 kg/m2 Hypertension Anxiety Race As thm a BMI ≥30 kg/m 2 Race As thm a Hyperlipidemia Education (>16 years) Substance abuse disorders Hyperlipidemia Cardiac arrhythmias Smoking status Diabetes Substance abuse disorders Education (>16 years) Diabetes Smoking status Cardiac arrhythmias Arthritis Arthritis Education (13-16 years) Schizophrenia Congestive heart failure Education (13-16 years) Dementia Stroke Schizophrenia Coronary artery disease Coronary artery disease Dementia Stroke Congestive heart failure Osteoporosis Cancer (all types) Cancer (all types) Osteoporosis Age at baseline Calendar year of baseline Calendar year of baseline Age at baseline

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.00 0.05 0.10 0.15 0.20 0.25 0.30

Absolute standardized differences Absolute standardized differences

Supplementary Figure 2. Balance of characteristics at baseline obtained using inverse probability weights for chronic kidney disease defined using eGFR levels, overall (left panel) and in women who underwent bilateral oophorectomy at age ≤45 years (right panel).

The red circles indicate the absolute standardized differences before balancing and the black diamonds indicate these differences after balancing using IPW. After the IPW adjustment, all of the standardized differences were below the recommended threshold of 0.10, denoting negligible imbalance of these characteristics. For each condition or characteristic, the absolute standardized difference is defined as the absolute value of the difference in means for that characteristic between women with and without bilateral oophorectomy, divided by the pooled standard deviation for that characteristic. The weights were derived from propensity scores estimated from logistic regression models including 17 chronic conditions present at baseline, years of education (unknown or ≤12, 13-16, >16), race (white vs nonwhite), body mass index (unknown or <30 vs ≥30 kg/m2), cigarette smoking (current or former vs never), and age and calendar year at baseline (continuous). These models were fit overall, and separately in each stratum to maximize the balance at the index date. Less than 1% of women with oophorectomy and no referent women fell outside the overlapping ranges (i.e., a wide region of common support). The propensity scores ranged between 0.15 and 0.87 for the overall women with oophorectomy and between 0.21-0.83 for referent women and between 0.06 and 0.91 for the women who underwent oophorectomy at age ≤45 years and between 0.13-0.88 for referent women. Weights greater than 10 were trimmed by setting these weights to the value of the 99th percentile for their respective group (bilateral oophorectomy or referent women). The weights were then stabilized to reduce variability by dividing each weight by the mean

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Supplemental material is neither peer-reviewed nor thoroughly edited by CJASN. The authors alone are responsible for the accuracy and presentation of the material. weight for their respective group. The stabilized IPW ranged between 0.6 and 3.3 for the overall group (0.6-3.3 for women with oophorectomy, 0.6-3.0 for referent women) and between 0.5 and 4.3 for the women age ≤45 years at baseline (0.5-2.2 for women with oophorectomy 0.6-4.3 for referent women).

Abbreviations: BMI, body mass index; COPD, chronic obstructive pulmonary disease; eGFR, estimated glomerular filtration rate; IPW, inverse probability weights. a Characteristics are presented in descending order of magnitude for each panel.

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