The Combined Use of Fractional Urate and Potassium Excretion in the Diagnosis of Diuretic-Induced Hyponatremia

Introduction Thiazide and loop-diuretics are among the most widely used drugs in the therapy of hypertension and chronic heart failure. Furthermore, hyponatremia is the most prevalent electrolyte imbalance affecting up to 25-30% of hospitalized patients while syndrome of inappropriate antidiuresis (SIAD) is involving approximately 35% of hyponatraemic inpatients. Clinical and laboratoristic algorithms support the differential diagnosis of hypotonic hyponatremia in actual guidelines of SIAD, but a potential bias is represented by the misleading clinical assessment of the extracellular volume status in diuretic-treated patients where the necessity of withdrawal of the therapy is mandatory. We investigated the role of fractional uric acid and potassium excretion (FEUA and FEK) in the differential diagnosis of hypotonic hyponatremia in SIAD and diuretic-treated patients. Methods Thirty-six SIAD, 30 thiazide-induced hyponatremia (TIH), and 32 diuretic-induced hyponatremia (DIH) patients were investigated calculating FEUA and FEK values in receiver operating characteristic (ROC) curve analysis to improve the diagnostic approach of hypotonic hyponatremia. Results The combination of the two investigated markers showed different significative results generating patterns useful to discriminate among the three different hyponatremic groups. Conclusion The fractional uric acid and potassium excretion could be considered as new markers in the diagnostic approach of hyponatremic diuretic-treated patients where classical algorithms could fail.