Chloride and Potassium Assessment are a helpful tool for Differential Diagnosis of Thiazide Associated Hyponatremia.

Abstract

Differential diagnosis of thiazide associated hyponatremia (TAH) is challenging. Patients can eitherhave volume depletion or a syndrome of inappropriate antidiuresis (SIAD)-like presentation. To evaluate the impact of the simplified apparent strong ion difference in serum (aSID), sodium + potassium-chloride) as well as the urine chloride and potassium score (ChU, chloride-potassium in urine) in the differential diagnosis of TAH, in addition to assessment of fractional uric acid excretion (FUA). Post-hoc analysis of prospectively collected data from June 2011 to August 2013. Hospitalized patients enrolled at University Hospital Basel and University Medical Clinic Aarau, Switzerland. 98 patients with TAH < 125 mmol/l were included, divided according to treatment response in volume-depleted TAH requiring volume substitution or SIAD-like TAH requiring fluid restriction. We computed sensitivity analyses with ROC curves. positive predictive value (ppv) and negative predictive value (npv) of aSID, ChU, and FUA in differential diagnosis of TAH. An aSID > 42 mmol/l had a ppv of 79.1% in identifying patients with volume-depleted TAH, whereas a value < 39 mmol/l excluded it with a npv of 76.5%. In patients for whom aSID was inconclusive, a ChU < 15 mmol/l had a ppv of 100% and a npv of 83.3% whereas FUA < 12% had a ppv of 85.7% and a npv of 64.3% in identifying patients with volume-depleted TAH. In patients with TAH, assessment of aSID, potassium and chloride in urine can help identifying patients with volume-depleted TAH requiring fluid substitution from patients with SIAD-like TAH requiring fluid restriction.