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Kidney Week

Abstract: PO0265

Histopathological Confirmation of Acute Tubular Injury in Patients with "Muddy Brown" Granular Casts in the Urinary Sediment

Session Information

Category: Acute Kidney Injury

  • 102 AKI: Clinical, Outcomes, and Trials

Authors

  • Varghese, Vipin, Department of Nephrology, Ochsner Clinic Foundation, New Orleans, Louisiana, United States
  • Ramanand, Akanksh, Department of Nephrology, Ochsner Clinic Foundation, New Orleans, Louisiana, United States
  • Velez, Juan Carlos Q., Department of Nephrology, Ochsner Clinic Foundation, New Orleans, Louisiana, United States
Background

Microscopic examination of the urinary sediment (MicrExUrSed) can be a useful tool in the differentiation of acute kidney injury etiology. In particular, “muddy brown” granular casts (MBGC) are thought to be pathognomonic for acute tubular injury (ATI). However, the ability of MBGC to predict biopsy-proven ATI has not been formally examined. Thus, we hypothesized that the identification of MBGC by MicrExUrSed can accurately predict a histopathological diagnosis of ATI.

Methods

In a single-center prospective study, we selected cases of patients seen in nephrology consultation who had a urine specimen subjected to MicrExUrSed as part of the clinical evaluation. Within this cohort, we identified cases in which a kidney biopsy was performed within 2 weeks of the MicrExUrSed. Presence of MBGC in those cases was determined. We assessed the performance of identification of MBGC for the diagnosis of biopsy-proven ATI. Sensitivity, specificity, negative predictive values (NPV), and positive predictive values (PPV) of MBGC to diagnose ATI were determined.

Results

Among 371 patients in whom MicrExUrSed was completed, 49 underwent kidney biopsy and were included. Mean age was 61 years, 38% were women. White race accounted for 59% and black race accounted for 33%. Mean serum creatinine was 3.4 mg/dL. Biopsy diagnosis was ATI in 36 (73%) and non-ATI in 13 (27%). Among the 36 cases of biopsy-proven ATI, concomitant glomerular pathology was present in 19 (53%). The sensitivity of MBGC for biopsy-proven ATI diagnosis was 78% (95% CI 61-90%), while the specificity was 100% (95% CI 75-100%). The PPV of MBGC for ATI diagnosis was 100% (95% CI 100%) and the NPV was 62% (95% CI 47-93%).

Conclusion

Our data demonstrate that MBGC on MicrExUrSed are pathognomonic for ATI confirmed by kidney biopsy – with high PPV and specificity of 100%. While MBGC reflect ATI, concomitant glomerular pathology can be present in patients with MBGC in the urine sediment.