Can the fractional excretion of uric acid distinguish the etiology of hyponatremia in patients taking diuretics?

Abstract

Measurement of the urinary sodium concentration can often help differentiate the various etiologies of hyponatremia. An elevated urinary sodium concentration is detected in the syndrome of inappropriate antidiuretic hormone (SIADH); however, the use of diuretics confounds the validity of this measurement. In this Practice Point commentary, I discuss the findings of Fenske et al., who suggest that the fractional excretion of uric acid (FEUA) is the best biomarker to determine whether hyponatremia is caused by SIADH in patients taking diuretics. An FEUA cutoff ≥12% had a positive predictive value of 100% for a diagnosis of SIADH in patients receiving diuretics, whereas an FEUA <8% excluded SIADH in this group. Here, I place the findings of Fenske et al. into clinical context, and discuss the utility of the FEUA and other biochemical markers for the diagnosis of SIADH in the presence of diuretics.