Fractional Excretion of Uric Acid?

All nephrologists, and most physicians and medical students are very familiar with the fractional excretion of sodium (FENa). The FENa (Urine Na x Plasma Creatinine / Plasma Na x Urine Creatinine) helps to differentiate the cause of acute renal failure (sorry, acute kidney injury). It is classically used in separating the differential diagnosis of AKI into three categories: pre-renal, intra-renal and post-renal.

A problem arises when a patient is on diuretics and renal perfusion is decreased. On diuretics, FENa is less accurate and useful. I have used the FE of urea in his setting. The utility of the FE Urea has been questioned, but is considered a better measurement in this circumstance. This month in the American Journal of Kidney Diseases, they report on the possibility of another calculation in these cases, the fractional excretion of uric acid (FEUA). The study was small (44 patientes) and needs to be validated, but the FEUA may just be more useful in the diagnosis of AKI caused by decreased kidney perfusion.