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Kidney Week

Abstract: SA-PO126

Fractional Excretion of Urea for the Differential Diagnosis of AKI: A Systematic Review and Meta-Analysis with Comparison to Fractional Excretion of Sodium

Session Information

Category: Acute Kidney Injury

  • 102 AKI: Clinical, Outcomes, and Trials


  • Abdelhafez, Mohammad O., Al-Quds University, Jerusalem, Palestine, State of
  • Hamadah, Abdurrahman M., St. Luke's Hospital, Duluth, Minnesota, United States
  • Gharaibeh, Kamel A., University of Maryland School of Medicine, Baltimore, United States

Group or Team Name

  • AQU Collaborators.

Differentiating between intrinsic and prerenal acute kidney injury (AKI) presents a challenge. This study aims to assess the performance of fractional excretion of urea (FEUrea) and compare it to fractional excretion of sodium (FENa) in distinguishing intrinsic from prerenal AKI.


We searched MEDLINE, Embase, CENTRAL, the Cochrane Library, and Scopus until July 2022. Studies evaluating FEUrea, with or without FENa, for differentiating AKI etiologies in adults were included. We assessed the methodological quality using the QUADAS-2/-C tools. We conducted a meta-analysis using the bivariate random effects model, with subgroup analyses to explore the impact of diuretic therapy on FEUrea performance. We performed direct statistical comparisons between FEUrea and FENa in the overall AKI patients and subgroups with and without diuretic therapy. Study protocol: PROSPERO, CRD42022341290.


We included 11 studies with 1108 hospitalized patients. Among 8 studies (915 patients) evaluating FEUrea at 35% threshold, the pooled sensitivity and specificity for distinguishing intrinsic from prerenal AKI were 66% (95% CI, 49-79%) and 75% (95% CI, 60-85%), respectively. In a subset of 6 studies (573 patients) comparing FEUrea at 35% to FENa at 1%, there was no significant difference in sensitivity (69% vs. 86%, P=0.089) but a significant difference in specificity (81% vs. 64%, P=0.038). Additionally, In 302 patients not on diuretics, there were no significant differences in sensitivity (77% vs. 89%, P=0.410) or specificity (80% vs. 79%, P=0.956). In 4 studies with 244 patients on diuretics, FEUrea demonstrated lower sensitivity (52% vs. 92%, P<0.001) but higher specificity (82% vs. 44%, P<0.001) compared to FENa.


Both FEUrea and FENa have limited utility in differentiating intrinsic from prerenal AKI. FEUrea does not provide a superior alternative to FENa, even in patients receiving diuretic therapy.