The Clinical Significance of the Fractional Excretion of Uric Acid and Urea in the Differentiation of Acute Kidney Injury

Jang, Jong Soon; Kim, Hee Sung; Lee, Shin Young; Lee, Seung Ho; Kim, Seung Jung; Kwon, Soon Kil; Kim, Hye Young

Abstract

PURPOSE:Fractional excretion of sodium (FENa) has been used in the differentiation of acute kidney injury (AKI) into traditional categories of prerenal azotemia (PR) and acute tubular necrosis (ATN). However, many patients with PR have already received diuretics or saline at the time of diagnosis, which increase FENa. In contrast, the fractional excretion of uric acid (FEUA) and urea (FEUN) is less influenced by diuretics. We investigated the diagnostic significance of the FEUA and FEUN in differentiating between PR and ATN.
METHODS
The FENa, FEUA, and FEUN were calculated in 40 patients with PR and 30 patients with ATN at day 0 (D0), day 1 (D1) and day 2 (D2), sequentially.
RESULTS
FEUA (PR 13.9+/-8.7% vs. ATN 33.2+/-27.0%, p<0.05) and FEUN (PR 32.1+/-18.9% vs. ATN 50.6+/-41.3%, p<0.05) were lower in PR than in ATN patients. At the cut-off value of 1% FENa, sensitivity and specificity for the detection of PR was 51.4% and 96.4%, respectively. When FENa, FEUA and FEUN were combined, sensitivity and specificity was 84% and100%, respectively. In the PR with FENa less than 1%, FENa significantly increased after treatment (D0 0.4+/-0.1% vs. D1 1.2+/-0.3% vs. D2 1.5+/-0.4 %, p<0.05), but FEUA and FEUN did not changed after treatment.
CONCLUSION
FEUA and FEUN may be useful in differentiating between PR and ATN. The combination of FENa, FEUA and FEUN might increase diagnostic sensitivity and specificity in the differential diagnosis of AKI.