Background:

Acute kidney injury (AKI) is a common presenting problem accounting for 1% hospital admission and also a major complication developing during in‐hospital stay for other reasons. Rapid identification and treatment of reversible causes of renal failure may improve patient outcome, reducing hospital and ICU stays and preventing progression to established renal failure. Traditionally fractional excretion of sodium (FENa) is used to discriminate acute tubular necrosis (ATN) from prerenal causes, but there are certain situations that render the FENa unreliable. In these circumstances, including diuretic use, a fractional excretion of uric acid (FEUA) can be measured, as it has been postulated to be unaffected by diuretics. Currently, there is a paucity of data addressing the validity of using the FEUA in AKI.

Methods:

To further examine this question, we designed a retrospective chart review. After institutional review board approval, charts were obtained from medical records of patients who had FEUA ordered. The study populations were all adult patients of all races hospitalized at OSF St. Francis Medical Center who had AKI. Patients with postrenal causes and acute interstitial nephritis were excluded. A total of 154 patients were grouped into prerenal AKI and ATN based on final diagnosis. Final diagnosis was based on improvement in renal function within a week or clinical documentation of recovery. The values of FEUA were then compared between the 2 groups. We also collected data on FENa when it was done. SPSS was used to run independent‐samples t tests to analyze the data.

Results:

Our lab reports FEUA < 12 as prerenal, 12–20 as indeterminate, and > 20 as ATN. An independent‐samples t test was conducted to compare prerenal AKI and ATN cases, and there was a significant difference in scores for prerenal (mean, 7.7; SD, 5.4) and ATN (mean, 21.9; SD, 13.2); t12 = 23.8, P = 0.002. These results show that FEUA is a good test to distinguish between prerenal AKI and ATN. Because it was a retrospective study, it did rely on the accuracy of written records, and there was a lack of blinding. We double‐checked the final diagnosis with improvement of renal function within days versus weeks.

Conclusions:

Good history, physical exam, vital signs, fluid status, and urine analysis remain key in the diagnosis of cause of AKI, but FENa and FEUA may assist in early diagnosis. FEUA may be a better tool that FENa in certain cases, and further prospective studies need to be designed to validate this retrospective analysis.

Disclosures:

K. Malhotra ‐ none; A. Bland ‐ none; G. S. Nace ‐ none