View and in Accordance with the and RTEC Casts (Rteccs) (2,3)

Original Investigation Diagnostic Utility of Serial Microscopic Examination of the Urinary Sediment in Acute Kidney Injury Vipin Varghese,1,2 Maria Soledad Rivera,1 Ali A. Alalwan,2 Ayman M. Alghamdi,2 Manuel E. Gonzalez,3 and Juan Carlos Q. Velez1,2 Abstract Background Microscopic examination of the urinary sediment (MicrExUrSed) is an established diagnostic tool for AKI. However, single inspection of a urine specimen during AKI is a mere snapshot affected by timing. We hypothesized that longitudinal MicrExUrSed provides information otherwise not identified in a single inspection. Methods MicrExUrSed was undertaken in patients with AKI stage $2 and suspected intrinsic cause of AKI seen for nephrology consultation over a 2-year period. MicrExUrSed was performed on the day of consultation and repeated at a second (2–3 days later) and/or third (4–10 days later) interval. Cast scores were assigned to each specimen. Chawla scores (CS) 3–4 and Perazella scores (PS) 2–4 were categorized as consistent with acute tubular injury (ATI), whereas CS 1–2 and PS 0–1 were categorized as nondiagnostic for ATI (non-ATI). Nonrecovering AKI was defined as a rise in serum creatinine (sCr) $0.1 mg/dl between microscopy intervals. Results At least two consecutive MicrExUrSed were performed in 121 patients (46% women, mean age 61614, mean sCr at consult of 3.361.9 mg/dl). On day 1, a CS and PS consistent with non-ATI was assigned to 64 (53%) and 70 (58%) patients, respectively. After a subsequent MicrExUrSed, CS and PS changed to ATI in 14 (22%) and 16 (23%) patients. Thus, 20%–24% of patients only revealed evidence of ATI after serial MicrExUrSed was performed. Patients with nonrecovering AKI were more likely to change their PS to the ATI category (odds ratio, 5.8; 95% CI, 1.7 to 19.3; P50.005 and positive likelihood ratio, 2.0; 95% CI, 1.3 to 2.9). Conclusions Serial MicrExUrSed revealed diagnostic findings of ATI otherwise not identified in a single examination. A repeat MicrExUrSed may be warranted in patients AKI of unclear etiology that are not recovering. KIDNEY360 2: 182–191, 2021. doi: https://doi.org/10.34067/KID.0004022020 Introduction these scores were designed on the basis of a single Microscopic examination of the urinary sediment examination of the urinary sediment. Although casts (MicrExUrSed) is a well-established clinical tool of provide valuable diagnostic clues, the natural history diagnostic and prognostic value in the evaluation of of cast formation remains unexplored. Thus, a single AKI (1–4). Specifically, the identification of renal tu- inspection of a urinary sediment specimen during AKI bular epithelial cells (RTECs) and granular casts (GCs) is a mere snapshot that depends on the day of ins- strongly suggest a diagnosis of acute tubular injury pection. Therefore, potential evidence of ATI can be (ATI) (5,6), the most common cause of acquired AKI in missed. We hypothesized that longitudinal MicrEx- the hospital setting (7). The abundance of “muddy” UrSed can provide additional diagnostic information fi brown GCs is considered a pathognomonic finding otherwise not identi ed in a single inspection. forATI.Overadecadeago,thefirst systematic approaches to grade findings from urinary sediment microscopy were developed. The Chawla score (CS) Materials and Methods and Perazella score (PS) were created with the inten- This study was conducted with approval from the fi tion to standardize the identi cation of GCs, RTECs, Institutional Board Review and in accordance with the and RTEC casts (RTECCs) (2,3). These scores demon- Declaration of Helsinki. Urine specimens were collected strated diagnostic and prognostic value in the evalu- from patients with AKI stage $2 (measured by Kidney ation of AKI due to ATI. The CS is determined by Disease: Improving Global Outcomes), who were seen assessing the percentage of low-power fields (LPFs) on consultation in an inpatient nephrology service over with GCs and RTECCs, whereas the PS is determined a2-yearperiodatOchsnerMedicalCenterwhenan by identifying the number of GCs in an LPF and the intrinsic etiology of AKI was suspected and members of number of RTECs in a high-power field. However, the research staff were available (8). 1Ochsner Clinical School, The University of Queensland, New Orleans, Louisiana 2Department of Nephrology, Ochsner Clinic Foundation, New Orleans, Louisiana 3Division of Nephrology, Department of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas Correspondence: Juan Carlos Q. Velez, 1514 Jefferson Highway, Clinic Tower 5th Floor, Rm 5E328, Ochsner Medical Center, New Orleans, LA 70121. Email: [email protected] 182 Copyright © 2021 by the American Society of Nephrology www.kidney360.org Vol 2 February, 2021 KIDNEY360 2: 182–191, February, 2021 Diagnostic Utility of Serial Microscopic Examination, Varghese et al. 183 Microscopic examination of the urinary sediment was microscopy was not uniformly completed for all of the performed as soon as possible, and always within 1 hour patients in the cohort. Microscopic examination of the uri- of sample collection. Once collected, specimens were kept at nary sediment was not repeated if the patient was anuric, room temperature and transferred to the laboratory. A 10 ml discharged, deceased, commenced hemodialysis, or there aliquot of urine was placed in a 15 ml high-clarity poly- was an inability to collect urine due to staffing or logistics. propylene conical tube and centrifuged at 8003 g for Urinary cast scores (CS and PS) for ATI were determined 5 minutes. The supernatant was poured off, and the pellet at each serial microscopy interval (Supplemental Tables 1 was resuspended by manual agitation in the remaining and 2) (5,6). A CS of 3–4andaPSof2–4 was categorized as 0.2 ml of supernatant. A plastic transfer pipette was used consistent with ATI, whereas a CS of 1–2 and PS of 0–1 was to place a single drop on a standard microscope slide, and categorized as nondiagnostic for ATI (Figures 1 and 2). a coverslip was placed over it. This process was done with To evaluate for factors influencing the probability of and without Sternheimer-Malbin stain (Kova, Garden conversion of the urine cast score from the non-ATI category Grove, California) (9). Then each sample was examined to the ATI category, we examined the course and timing of by a trained operator using a Nikon Eclipse E200 micro- AKI. Thus, we defined nonrecovering AKI as a rise in serum scope (Melville, New York) with 103 and 403 magnifica- creatinine $0.1 mg/dl at the time of either the second or tion objectives, and a 103 magnification eye-piece. The third serial microscopy compared with the serum creatinine entirety of the slide was examined at both LPF (1003 on the day of the first microscopy. When the serum creat- magnification) and high-power fields (4003 magnification). inine trends down even by 0.1 mg/dl, most clinicians in- Representative images of all sample slides were taken using terpret it as a positive trajectory and the initial diagnostic an Apple iPhone 6S camera (Cupertino, California) and suspicion is typically not challenged. However, when serum LabCam microscopy adaptor (iDu Optics, New York, creatinine does not decrease, the practicing clinician might New York) on a Leica CME microscope (Buffalo Grove, be interested in reassessing the tentative diagnosis. In ad- Illinois). At least two operators independently assessed and dition, we arbitrarily defined early period of AKI as the first scored each specimen, one operator was blinded to the 6 days after the onset of AKI and late period of AKI as clinical data and one was unblinded. Operators included $7 days since the onset of AKI. nephrologists, nephrology fellows, internal medicine resi- A presumptive etiology of AKI was determined on the dents, and medical students who were trained to determine basis of available clinical information as previously reported both PS and CS. (10): ischemic ATI was considered in patients when AKI Microscopic examination of the urinary sediment was occurred after hemodynamic instability (shock, hypoten- first performed on the day of consult (day 1). Then, a sub- sion, large fall in systolic BP, tachyarrhythmia, bradyar- sequent serial MicrExUrSed was attempted to be performed rhythmia), volume depletion unresponsive to intravenous at a second time interval defined as days 2–3 from the day of expansion or exposure to vasomotor drugs (angiotensin the consult, and/or at a third time interval defined as day converting enzyme inhibitors, angiotensin receptor block- 4–10 from the day of the consult. A second and third serial ers, calcineurin inhibitors) that did not resolve on drug A B C D E F Figure 1. | Representative photomicrographs illustrating the application of the Perazella score (PS) to grade urinary sediment slides for elements of acute tubular injury (ATI). (A and B) PS of 1: 1–5 granular casts (GC) per low-power field (LPF) with no evidence of renal tubular epithelial cells (RTECs); (C) PS of 2: $6 GCs with no evidence of RTECs; (D and E) PS of 3: $6 GCs with 1–5 RTECs (blue arrows, assessed at high-power field [HPF]); and (F) PS of 4: $6 GCs with $6 RTECs. 184 KIDNEY360 A B CD Figure 2. | Representative photomicrographs illustrating the application of the Chawla score (CS) to grade urinary sediment slides for elements of acute tubular injury (ATI). (A) CS score of 1: no evidence of granular casts (GC) or renal tubular epithelial cell casts (RTECC); (B) CS of 2: at least one GC or ECC on ,10% of low-power fields (LPFs); (C) CS of 3: many GC or RTECC on 10%–90% of LPFs (bottom left, RTECC at LPF, bottom right: RTECC at high-power field (HPF), both with Sternheimer-Malbin stain); (D) CS score of 4: sheets of muddy brown GCs, with GC on .90% of LPFs.

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