Venous Thromboembolism According to Age the Impact of an Aging Population

Home , Doppler ultrasonography, Scintigraphy

ORIGINAL INVESTIGATION Venous Thromboembolism According to Age The Impact of an Aging Population

Paul D. Stein, MD; Russell D. Hull, MBBS, MSc; Fadi Kayali, MD; William A. Ghali, MD, MPH; Andrew K. Alshab, MD, MPH; Ronald E. Olson, PhD

Background: With the aging of the US population, there the use of diagnostic tests over 21 years were markedly is concern that the rate of venous thromboembolism will higher in elderly than in younger patients (PϽ.001). Al- increase, thereby increasing the health burden. In this though the rate of diagnosed DVT in elderly patients strik- study we sought to determine trends in the diagnosis of ingly increased over the past decade (PϽ.001), that of deep venous thrombosis (DVT) and pulmonary embo- PE has been relatively constant. There was a proportion- lism (PE) in the elderly as well as the use of diagnostic ately greater use of venous ultrasonography, ventilation- tests. perfusion lung scanning, and pulmonary angiography in elderly than in younger patients. Methods: Data from the National Hospital Discharge Survey were used. These data are abstracted each year Conclusions: Extensive use of diagnostic tests in el- from a sample of records of patients discharged from non- derly patients in the past decade has resulted in an in- federal short-stay hospitals in the entire United States. creased diagnostic rate for DVT but not PE. The reason Main outcome measures were trends in rates of diagno- for this disparity is uncertain but may reflect early diag- sis of DVT and PE as well as trends in the use of diagnosis and treatment of DVT. With the aging of the popu- nostic tests between 1979 and 1999. lation, DVT will increase the health burden.

Results: The rates of diagnosis of DVT and PE and of Arch Intern Med. 2004;164:2260-2265

HE POPULATIONS OF THE tion of patients with DVT and/or PE in the Western industrialized United States, which avoids the bias that can countries are aging, and it occur with regional, often less diverse, is predicted that the el- samples. The size of the NHDS database and derly population will in- the broad representation it affords make it creaseT from 26.6 million in 2003 to 36.0 well suited to assess trends in the rate of ve- million by 2020 in the United States—a nous thromboembolic disease in the United 35% increase.1 The risk of venous throm- States over 2 recent decades. boembolism is strongly associated with In view of the paucity of empirical na- age.2-4 Furthermore, deep venous throm- tional literature for venous thromboembo- bosis (DVT), which leads to pulmonary lism in the elderly and the scope provided Author Affiliations: embolism (PE), is the third most com- by the NHDS database, we analyzed (1) 21- Department of Research, mon cardiovascular disease after myocar- year diagnostic trends for DVT and PE; (2) St Joseph Mercy Oakland 5 Hospital, Pontiac, Mich, dial infarction and stroke. Yet, neither the diagnostic process involved; and (3) (Drs Stein, Kayali, and Alshab) trends in the rates of diagnosis of DVT and changes in the proportion of elderly per- Department of Internal PE in the elderly nor trends in the rates sons with PE and DVT in the US popula- Medicine, Wayne State of use of diagnostic tests in the elderly have tion between 1979 and 1999. By providing University, Detroit, Mich been assessed using a survey of the entire a representative hospital survey that per- (Dr Stein); Departments of United States. mits accurate estimates of rates of PE and Medicine (Drs Hull and Ghali) To assess the public health burden of DVT in the population, the NHDS is and Community Health DVT and PE in the elderly, we evaluated the uniquely suited to evaluate trends over time Services (Dr Ghali), University database of the National Hospital Dis- in the rates of diagnosis of DVT and PE of Calgary, Calgary, Alberta; and 6,7 Department of Grants, charge Survey (NHDS) , one of the larg- among the elderly. We present an epide- Contracts, and Sponsored est known databases of records of patients miological study of hospitalized elderly per- Research, Oakland University, hospitalized with PE and/or DVT. This sur- sons in the United States assessing the bur- Rochester, Minn (Dr Olson). vey allows for a methodologically rigorous den of venous thromboembolism over the Financial Disclosure: None. sample, distributed over the entire popula- recent 20-year interval.

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Downloaded From: https://jamanetwork.com/ on 10/01/2021 METHODS STATISTICAL ANALYSIS The rates of diagnosis of DVT and PE were calculated by di- DATA SOURCES viding the number of individuals having the conditions in a given period by the sum of the yearly census estimates of the US popu- Data from the NHDS were used for this study.6 The NHDS da- lation in the same period and reporting the number per 100000 tabase is described in detail elsewhere.7-25 The survey design, population. The numerator was obtained from the NHDS. The sampling, and estimation procedures were planned to pro- denominator was obtained from estimates based on the US cen- duce calendar-year estimates. Trained medical personnel coded sus, as described. Yearly rates of diagnosis of DVT and PE were diagnoses and procedures using the International Classifica- calculated for the 21-year period of observation. Descriptive sta- tion of Diseases, Ninth Revision, Clinical Modification (ICD-9- tistics were used to graphically display trends over time in rates CM).26 A minimum of 1 and a maximum of 7 diagnostic codes of diagnosis of DVT and PE and rates of use of diagnostic tests. were assigned for each sample abstract. If an abstract included These data show estimated rates of diagnosis or rates of use of surgical and/or diagnostic procedures, a maximum of 4 pro- diagnostic tests based on sampling rather than on a census of cedure codes was assigned. cases or procedures. Linear regression analyses were performed to calculate the 28 NHDS SAMPLING SCHEME slopes of selected segments of the curves describing the data. Pearson correlation analyses were performed for the same linear segments to assess the extent of dispersion of points around The NHDS is based on a national probability sample of pa- 28 tients discharged from short-stay hospitals—exclusive of fed- the regression lines. More complex equations were used to de- eral, military, and Department of Veterans Affairs hospitals— scribe the curves that related rate ratios for DVT and PE to age. located in the 50 States and the District of Columbia. The Linear regression analyses were performed using InStat soft- sampling plan, performed in 3 stages, is described else- ware, version 3.0 (GraphPad Software, San Diego, Calif), and where.6,7,27 nonlinear analyses were performed using SPSS software, version 11.0 (SPSS Inc, Chicago, Ill). Differences between groups and differences in the rates of ESTIMATION PROCEDURES use of diagnostic tests performed over time were assessed using t tests when 2 groups were compared and analysis of vari- Estimates of patients with DVT and PE and the total number ance when multiple groups were compared.28 Differences of rates of diagnostic tests performed in the entire United States for DVT were assessed by ␹2 test. An analysis of covariance was done and PE were derived from the number of sampled patients with with sex and race (white and black races only) as covariates DVT and/or PE and the number of diagnostic tests performed using SPSS software, version 11.0. The adjusted values based in sampled patients using a multistage estimation procedure. on the covariates for DVT per 100000 population per year were This procedure, which produces essentially unbiased national submitted to a linear regression analysis. estimates, is described elsewhere.7,27 RESULTS IDENTIFICATION OF DVT CASES

All available diagnostic code fields were screened for specific TRENDS IN THE RATE OF DVT DIAGNOSIS codes to identify patients with DVT and/or PE. Since 1979, the ICD-9-CM has been used for classifying diagnoses and proce- Trends for the 21-year study period show that the rate dures in the NHDS. Although the ICD-9-CM is modified an- of diagnosis for DVT in elderly patients (Ն70 years) was nually, the diagnostic codes for “PE and infarction” and “phle- constant from 1979 to 1990 but increased markedly from bitis and thrombophlebitis of deep vessels of lower extremities” 1990 to 1999. The rate of DVT diagnoses was higher for have changed little. elderly patients (Ն70 years) than for younger patients The specific ICD-9-CM codes that we used for identifica- (20-69 years old) (rate ratio, 4.72; 95% confidence in- tion of patients with PE were 415.1, 634.6, 635.6, 636.6, 637.6, Ͻ Figure 1 638.6, and 673.2. The codes used for identification of patients terval, 4.30-5.14; P .001) ( A). The rate of DVT with DVT were 451.1, 451.2, 451.8, 451.9, 453.2, 453.8, 453.9, diagnoses among elderly patients increased from 454 per 671.3, 671.4, and 671.9. Five-digit codes, such as 451.11 (in- 100000 population in 1990 to 655 per 100000 popula- cluded under the code 451.1), were not listed because they were tion in 1999 (Figure 1A). included under the corresponding 4-digit codes. The ICD- The 21-year trends for diagnosing DVT according to 9-CM codes used for diagnostic tests were the following: 88.77 age distribution (by 10-year increments) are shown in for diagnostic ultrasound examination of the peripheral vas- Figure 1B. The greatest use of diagnostic tests during the cular system (DVT ultrasonic scanning); 88.43 for arteriogra- past decade occurred among the elderly population. phy of pulmonary arteries; 88.66 for venography of the lower extremities; and 92.15 for pulmonary radioisotopic scanning. TRENDS IN THE RATE OF PE DIAGNOSIS

CALCULATION OF RATES OF DVT AND PE Trends for the 21-year study period show that the rate of PE diagnosis was greater among elderly patients (Ն70 We calculated the rates of DVT and PE in the general popula- years) than among younger patients (20-69 years old) (rate tion. The population estimates were derived from the US Bu- Ͻ reau of the Census estimates of national, state, and county resi- ratio, 6.20; 95% confidence interval, 5.74-6.65; P .001) dent populations.7 Estimated populations according to age and (Figure 2A). Among elderly patients, the rate of PE di- projected population estimates were obtained from the Cen- agnosis decreased from 370 per 100000 population in ters for Disease Control and Prevention CDC WONDER data- 1979 to 254 per 100000 population in 1990 (Figure 2A). base.1 From 1990 to 1999, the rate was constant among those

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800 400 ≥ ≥ Age 70 y Age 70 y Age 20-69 y Age 20-69 y 600 300 000 Population 400 200 000 Population

200

DVT per 100 100 0 19791981 1983 198519871989 1991 1993 1995 1997 1999 PE per 100

0 19791981 1983 198519871989 1991 1993 1995 1997 1999 B

1000 B Age 70-89 y Age 40-49 y Age 60-69 y Age 20-39 y 500 800 Age 70-89 y Age 40-49 y Age 50-59 y Age 60-69 y Age 20-39 y Age 50-59 y 600 400 000 Population 400 300

200 000 Population

200 DVT per 100 0 19791981 1983 198519871989 1991 1993 1995 1997 1999

Year PE per 100 100

Figure 1. Deep venous thrombosis (DVT) per 100000 population. A, Among 0 19791981 1983 198519871989 1991 1993 1995 1997 1999 elderly patients (Ն70 years), the rate of diagnosis of DVT was constant from 1979 to 1990 and increased from 1990 to 1999 (slope=25.1 DVT per 100000 Year population yearly; r =0.929; PϽ.001). In younger patients (20-69 years old), there was a slight but significant decline in the DVT rate between 1979 and Figure 2. Pulmonary embolism (PE) per 100000 population. A, Among 1990 (slope=−3.46 DVT per 100000 population yearly; r =−0.911; PϽ.001); elderly patients (Ն70 years), the rate of diagnosis of PE decreased from the rate then increased somewhat between 1990 and 1999 (slope=3.71 DVT 1979 to 1990 (slope=−12.4 PE per 100000 population yearly; r =−0.889; per 100000 population yearly; r =0.916; PϽ.001). B, From 1979 to 1990 the PϽ.001) and then remained constant from 1990 to 1999. In younger rate of diagnosis of DVT was constant in patients aged 60 to 69 years and 70 to patients (20-69 years old) there was a slight but significant decline in the PE 89 years. During this period the rate decreased in younger age groups (P=.01 rate between 1979 and 1990 (slope=−3.06 PE per 100000 population yearly; to PϽ.001), and from 1990 to 1999 the rate increased in all age groups (P=.02 r =−0.946; PϽ.001); the rate then increased somewhat from 1990 and 1999 to PϽ.001). (slope=0.996 PE per 100000 population yearly; r =0.847; P=.002). B, In all age groups the rate of diagnosis of PE significantly decreased from 1979 to 1990 (P=.01 to PϽ.001). From 1990 to 1999, the rates remained constant 70 years or older whereas it declined significantly among in all age groups except in the 20- to 39-year-old age group, whose rate younger patients (20-69 years old), from 67 PE diag- increased slightly. noses per 100000 population in 1979 to 30 per 100000 population in 1990. From 1979 to 1990, the rate of PE diagnosis de- many more venous ultrasound tests of the lower extremi- creased in all age groups (Figure 2B). From 1990 to 1999, ties were performed in the elderly population (Ն70 years) it was constant in all age groups but 1—that of patients than in the younger population (20-69 years old) (rate aged 20 to 39 years, for which it increased slightly. ratio, 5.72; 95% confidence interval, 5.70-5.75; PϽ.001) (Figure 4A). INFLUENCE OF SEX AND RACE The rate ratio of the use of ultrasound tests, obtained by comparing the rate for each age decade with the rate The rates of diagnosis of DVT or PE were similar for el- for the group aged 20 to 29 years (based on mean 1989- derly men and women and for elderly blacks and whites. 1999 values), was highest in elderly patients (Figure 4B). Trend analysis shows similar diagnostic rates during the The rate of use of lung scans for the 21-year study pe- 21-year interval. Covariate analysis for race and sex shows riod was highest in elderly patients (PϽ.001) (Figure 5A). no effect of race (black or white) or sex on the increas- However, lung scan use declined in all age groups as Dop- ing rate of DVT in the elderly. pler ultrasonography became common. The rate of pulmonary angiography for the 21-year DIAGNOSTIC TESTS FOR DVT AND PE study period was higher in elderly than in younger pa- ACCORDING TO AGE tients (PϽ.001) (Figure 5B). Pulmonary angiography use increased from 1979 to 1999 for both elderly and younger The use of contrast venography of the lower extremities patients. was higher in elderly than in younger patients (PϽ.001) (Figure 3). Venography use sharply declined DIAGNOSIS OF DVT AND PE from the late 1980s to the late 1990s, as the use of ultra- ACCORDING TO AGE sonography increased. Between 1989 and 1999, when venous ultrasonogra- Comparing the rates of diagnosis of DVT at each decade phy of the lower extremities was commonly available, of age with the rate for those aged 20 to 29 years, the rate

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Downloaded From: https://jamanetwork.com/ on 10/01/2021 ratio increased exponentially up to age 89 years 200 (Figure 6A). In patients aged 70 to 79 years and 80 to Age ≥70 y 89 years, the rate ratios for diagnosis of DVT were 12.7 Age 20-69 y and 17.7, respectively. 150 000 Population

Comparing the rates of diagnosis of PE at each decade of age with the rate for those aged 20 to 29 years, 100 the rate ratio increased exponentially up to age 89 years (Figure 6B). In patients aged 70 to 79 years and 80 to 89 50 years, the rate ratios for PE diagnosis were 20.6 and 27.9,

respectively. per 100 Venograms 0 19791981 1983 198519871989 1991 1993 1995 1997 1999 Year TRENDS IN POPULATION GROWTH Figure 3. Contrast venography use was higher in elderly than in younger Between 1990 and 2003, the elderly population in the patients (PϽ.001). United States increased by 5.4 million (an increase from 8.5% of the population to 9.4% of the population). By A Age ≥70 y 2020 the elderly population is predicted to increase by 300 Age 20-69 y an additional 9.4 million, to become 11.0% percent of the general population. 200 COMMENT 000 Population

100 Although a striking upward trend in the rate of diagno- per 100 sis of DVT was observed among elderly patients during Ultrasonographic Scanning the past decade, the rate of diagnosis of PE remained con- 0 stant in that population. Upward trends in the rate of di- 19791981 1983 198519871989 1991 1993 1995 1997 1999 agnosis for DVT were more prominent with each increas- Year

ing decade of age from 1990 to 1999. In contrast, the rate B of diagnosis for PE was generally constant and did not 30 show consistent, substantive increases in that decade. The 25.3 reason for this disparity is uncertain but may reflect early 20.4 20 diagnosis and treatment of DVT. 14.6 Diagnostic approaches for DVT and PE have changed 8.4 markedly over the past 2 decades, in temporal harmony Rate Ratio 10 27,29 4.8 2.5 with the evolving literature. Our findings in the el- 1.4 derly reflect the diagnostic changes in clinical practice. Over 0 the past decade, Doppler ultrasonography has supplanted 20-2930-39 40-49 50-59 60-69 70-79 80-89 90-99 ascending contrast venography as the preferred diagnos- Age Group, y tic approach for DVT, and lung scanning has sharply declined as Doppler ultrasonography became established as Figure 4. Use of ultrasonography by age group (1979-1999). A, Doppler a diagnostic test. Pulmonary angiography use in the el- ultrasonography use in elderly patients markedly increased after 1982 and stabilized in the 1990s. B, Rate ratios increased exponentially with age derly increased over the past 2 decades. Recently, spiral- (95% confidence intervals are too narrow to display). computed tomography has emerged as a popular (but yet to be proven) diagnostic test for PE. As this test became widely available only in the late 1990s, it is unlikely that spectrum of hospitalized patients rather than specific its use has been indirectly captured by our trend analy- populations (eg, populations undergoing general or or- sis.30,31 An effect in the late 1990s, however, cannot be ex- thopedic surgery). The exponential increase with age in cluded. Impedance plethysmography was not included the rate of diagnosis for DVT and PE in the elderly em- among the diagnostic tests for DVT because our data show phasizes the impact of aging on the epidemiology of ve- that only 1.4% of leg tests were obtained with this method. nous thromboembolism. Our findings are consistent with Even during its period of peak use, in 1987, only 3.5% of those of regional surveys performed in the United States.2,3 diagnostic tests for DVT were done with impedance ple- The NHDS database provides a valid measure of the chal- thysmography. lenges facing the US health care system with respect to An abundance of literature documents that the risk the risk of DVT and PE with aging. of venous thromboembolism increases with age.2-5,32-43 Our Recommendations for prophylaxis in surgical pa- 21-year analysis, which captures the findings for ve- tients are partially based on the age of the patient.44 Pa- nous thromboembolism for hospitalized patients, strongly tients younger than 40 years are considered at low risk endorses this prior knowledge. The dramatic change in for venous thromboembolism for specific in-hospital sur- the risk for DVT or PE with increasing age documented gical groups, but being older than 40 years is consid- by our analysis of the NHDS database is based on a na- ered a more important risk factor.44 This has led to the tional rather than regional database and includes a broad general sense that age as a risk factor has a break point

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400 30 000 Population

300 20 17.7 17.9 200

Rate Ratio 12.7

8.1 100 10 4.6 1.7 2.7 Lung Scans per 100 0 19791981 1983 198519871989 1991 1993 1995 1997 1999 0 20-2930-39 40-49 50-59 60-69 70-79 80-89 90-99 B 40 Age ≥70 y B Age 20-69 y 40

30 27.9 27.3 000 Population

20 20.6 20 10 Rate Ratio 11.7

10 6.1 Angiograms per 100 0 3.1 1979-1981 1982-1984 1985-1987 1988-1990 1991-1993 1994-1996 1997-1999 1.7 Year 0 20-2930-39 40-49 50-59 60-69 70-79 80-89 90-99 Age Group, y Figure 5. Use of lung scans and pulmonary angiography by age group (1979-1999). A, Radioisotopic lung scan use was highest in elderly patients (Ն70 years) (PϽ.001). B, The rate of use of pulmonary angiograms was Figure 6. Rate ratios for the diagnosis of deep venous thrombosis (DVT) and higher in elderly patients (PϽ.001). pulmonary embolism (PE) were averaged over 21 years. A, The rate ratios for the diagnosis of DVT increased exponentially (95% confidence intervals were too narrow to display). B, The rate ratios for the diagnosis of PE increased at 40 years. Our data provide further insight into the risk exponentially (95% confidence intervals were too narrow to display). of venous thromboembolism in the younger in-hospital population. Indeed, patients aged 30 to 39 years have al- ing diagnostic procedure occurrences.45 The consequence most a 2-fold increase in the risk of DVT or PE com- of a lower sensitivity is that the absolute values shown pared with younger patients. The concept that the el- on the trend curves, especially for the diagnostic tests, derly are at the greatest need for thromboprophylaxis is are an underestimate of the actual values. In contrast, the emphasized by our data, which show a 18- to 28-fold in- directional trends and the relative positions of the curves crease in the risk for DVT or PE in patients 70 years or described herein are likely to be correct. The potential older compared with those aged 20 to 29 years. for variation in sensitivity of coding over time repre- In an effort to include all patients with DVT or PE, sents a possible threat to the validity of our findings. In we used some codes that are nonspecific (451.8 phlebi- particular, 2 phenomena may have introduced variabil- tis and thrombophlebitis of other sites and 451.9 phle- ity into the sensitivity of coding: DRG creep and changes bitis and thrombophlebitis of unspecified sites). Code over time to the ICD-9-CM coding system. In the early 451.8 includes not only the iliac vein but also thrombo- 1980s, the Health Care Financing Administration intro- phlebitis of the breast. However, thrombophlebitis of the duced DRGs as a mechanism for reimbursing hospitals breast constituted only 3% of all DVTs. Regarding codes providing care to Medicare recipients. Hospital admin- 634.6, 635.6, 636.6, 637.6, and 638.6 (embolism dur- istrations rapidly recognized that reimbursement was di- ing abortion), some women with nonthromboembolic em- rectly linked to the extent of coding for individual pa- bolism were included. However, among women aged 10 tients.47 The phenomenon of DRG creep is thus an artifact to 54 years who had PE, only 0.8% had embolism dur- of coding that might have increased the sensitivity of coding abortion. ing when this method of reimbursement was intro- Several additional methodological issues require con- duced.45 The trends that we report do not appear to have sideration. They concern the sensitivity and specificity45 of been affected by DRG creep because, for middle-aged and the NHDS summary sheet for capturing diagnostic test use, younger patients, the trends for DVT and PE decreased the “upcoding” of diagnoses and procedures that occurs or were static. As for the issue of changes over time to over time (a phenomenon referred to as the Diagnosis- the ICD-9-CM coding system, there were no confound- Related Group [DRG] “creep”),46 and changes over time ing changes to the coding scheme for PE, DVT, or asso- in the ICD-9-CM coding system. The specificity of the ICD- ciated procedures during the 21-year interval studied. 9-CM coding system is high. Thus, most of the proce- Thus, it is unlikely that changes to ICD-9-CM perturb our dures that were coded in discharge abstracts were actually findings. A minor issue, which concerns a minimal num- carried out. The frequencies, however, are underreported ber of procedures, is the atypical use of a diagnostic pro- because of the imperfect sensitivity of coding for captur- cedure. Ventilation-perfusion lung scanning prior to tho-

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Downloaded From: https://jamanetwork.com/ on 10/01/2021 racic surgery and pulmonary angiography for chronic 16. Graves EJ. Detailed diagnoses and procedures, National Hospital Discharge pulmonary hypertension are 2 examples of atypical pro- Survey, 1990. Vital Health Stat 13. 1992;113:1-225. 17. Graves EJ. Detailed diagnoses and procedures, National Hospital Discharge cedure use, and noninvasive or less invasive diagnostic Survey, 1991. Vital Health Stat 13. 1994;115:1-290. tests performed in the outpatient setting may have re- 18. Graves EJ. Detailed diagnoses and procedures, National Hospital Discharge sulted in an underestimate of the atypical use of these Survey, 1992. Vital Health Stat 13. 1994;118:1-281. procedures. Outpatient treatment of DVT is unlikely to 19. Graves EJ. Detailed diagnoses and procedures, National Hospital Discharge have affected the findings during the 21-year interval stud- Survey, 1993. Vital Health Stat 13. 1995;122:1-288. 20. Graves EJ, Gillum BS. Detailed diagnoses and procedures, National Hospital ied. It is recognized that hospital discharge data incom- Discharge Survey, 1994. Vital Health Stat 13. 1997;127:1-145. pletely capture many diagnoses and procedures. We em- 21. Graves EJ, Gillum BS. Detailed diagnoses and procedures, National Hospital phasize directional trends and relative differences, rather Discharge Survey, 1995. Vital Health Stat 13. 1997;130:1-146. than absolute values, in the rates of diagnosis. 22. Graves EJ, Kozak LJ. Detailed diagnoses and procedures, National Hospital Discharge Survey, 1996. Vital Health Stat 13. 1998;133:1-151. In conclusion, our findings support the literature and 23. Owings MF, Lawrence L. Detailed diagnoses and procedures, National Hospital emphasize that a disproportionately high risk of thrombo- Discharge Survey, 1997. Vital Health Stat 13. 1999;145:1-157. embolic disease occurs with age. Diagnostic approaches to 24. Popovic JR, Kozak LJ. National Hospital Discharge Survey: annual summary 1998. DVT and PE in the elderly have changed markedly in tem- Vital Health Stat 13. 2000;148:1-194. poral harmony with the evolving literature,27,29 and our find- 25. Popovic JR. 1999 National Hospital Discharge Survey: annual summary with detailed diagnosis and procedure data. Vital Health Stat 13. 2001;1-151:1-206. ings on diagnostic trends capture this change. 26. Jones ML, Brouch KL, Allen MM, Aaron WE, eds. St Anthony’s ICD-9-CM Code Book. Alexandria, Va: St Anthony Publishing Inc; 1991. Accepted for Publication: December 16, 2003. 27. Stein PD, Hull RD, Ghali WA, et al. Tracking the uptake of evidence: two decades Correspondence: Paul D. Stein, MD, Saint Joseph Mercy of hospital practice trends for diagnosing deep vein thrombosis and pulmonary embolism. Arch Intern Med. 2003;163:1213-1219. Oakland Hospital, 44505 Woodward Ave, Pontiac, MI 28. Glantz SA. Primer of Biostatistics. New York, NY: McGraw-Hill; 1981. 48341-3244 ([email protected]). 29. Tapson VF, Carroll BA, Davidson BL, et al; American Thoracic Society. The di- Acknowledgment: We thank Robert Pokras, MA, Cen- agnostic approach to acute venous thromboembolism: clinical practice guideline. ters for Disease Control and Prevention, National Cen- Am J Respir Crit Care Med. 1999;160:1043-1066. ter for Health Statistics, Hyattsville, Md, for his assis- 30. Remy-Jardin M, Remy J, Dechildre F, et al. Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scintigraphy. tance. We also thank Rita Biel, BSc, and Jeanne Sheldon, Radiology. 1996;200:699-706. BA, for their assistance with this manuscript. 31. Teigen CL, Maus TP, Sheedy PF II, et al. Pulmonary embolism: diagnosis with electron-beam CT. Radiology. 1993;188:839-845. 32. Nordstrom M, Linblad B, Bergqvist D, Kjellstrom T. 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