Abstract: TH-PO103
Low Fractional Excretion of Urinary Sodium Is a Common Finding During Acute Tubular Injury Presenting with Abundant Muddy Brown Granular Casts
Session Information
- AKI: Biomarkers, Drugs, Onco-Nephrology
November 07, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Acute Kidney Injury
- 102 AKI: Clinical, Outcomes, and Trials
Authors
- Rivera, Maria Soledad, The University of Queensland, New Orleans, Louisiana, United States
- Velez, Juan Carlos Q., The University of Queensland, New Orleans, Louisiana, United States
Background
Fractional excretion of urinary sodium (FENa) remains the most widely utilized diagnostic test in clinical practice for the evaluation of acute kidney injury (AKI). A low FENa (<1%) is considered consistent with prerenal azotemia and not due to overt acute tubular injury (ATI). However, presence of muddy brown granular casts (MBGCs) during microscopic examination of the urinary sediment (MicrExUrSed) are deemed pathognomonic of ATI. We hypothesized a lack of concordance between the two tests.
Methods
We conducted a prospective observational study in patients seen in the inpatient nephrology consultation team with AKI stage ≥ 1 (AKIN) over a 1.5-yr period. On the day of the consult and 48 hrs later, MicrExUrSed was performed to determine the percentage of low power fields (lpf) containing MBGCs. FENa was calculated on the same day to compare it with MBGCs abundance. Outcome measure was ≥ 50% increase from baseline serum creatinine (sCr) at discharge.
Results
Both FENa and presence of MBGCs by MicrExUrSed was completed in 135 patients, 57 (42%) were female, median age was 59 (25 - 88). The median sCr at the time of AKI was 3.2 (2.5 - 4.6) mg/dL. The etiology of AKI (pure de novo AKI 57%, AKI on CKD 43%) was ischemic ATI (40%), toxic ATI (15%), ischemic/toxic ATI (19%) and others (27%). MBGCs were found in 71 patients (53%) in our cohort. Among those, 56 (42%) and 32 (24%) had >10% and ≥50% lpf with MBGCs, respectively. FENa was <1% in 24/56 (44%) and 13/32 (41%) of those with >10% and ≥50% lpf with MBGCs, respectively. Thus, the concordance between FENa and MicrExUrSed for ATI diagnosis was deemed poor (estimated kappa coefficient 0.3018). In addition, ≥50% lpf with MBGCs was associated with greater risk for ≥ 50% increase from baseline sCr at discharge [relative risk (RR) 1.5, CI 1.1 – 2.0, p = 0.012], whereas FENa >1% did not predict that outcome [RR 1.1, CI 0.8 – 1.5, p = 0.39].
Conclusion
Close to half of the patients in our cohort who exhibited abundant MBGCs during MicrExUrSed presented with FENa <1%. “Sheets” of MBGCs were associated with greater risk for more sustained elevation in sCr after AKI, whereas FENa >1% was not predictive. These data strongly suggest that sole reliance in low FENa to exclude ATI should be abandoned and MicrExUrSed should be pursued for AKI diagnosis.