The Role of Fractional Excretion of Uric Acid in the Differential Diagnosis of Hypotonic Hyponatraemia in Patients with Diuretic Therapy.

Vincenzo Bassi,Olimpia Fattoruso

doi:10.7759/cureus.7762

Abstract

Hyponatraemia is the most common electrolyte imbalance found in hospital population and worldwide thiazide and loop-diuretics are among the most widely used drugs. Syndrome of inappropriate antidiuresis diagnosis (SIAD) is complicated in the presence of diuretic therapy due to the misleading clinical assessment of the extracellular volume status, and in order to make SIAD diagnosis it is often necessary to withdraw diuretic therapy. Our study aimed to investigate the diagnostic role of these alternative markers of volume status, serum uric acid (sUA) and fractional excretion of uric acid (FEUA), in hyponatraemic patients treated with different diuretic drugs. Eighty-nine patients were enrolled with the diagnosis of SIAD, diuretic-induced hyponatremia (DIH, treated with furosemide and potassium canrenoate) or thiazide-induced hyponatremia (TIH, treated with hydrochlorothiazide, metolazone or indapamide) and investigated with receiver operating characteristic analysis and a sensitivity test. Our results show that FEUA discriminated better than sUA between SIAD and DIH patients (area under curve 0.96, <0.001 vs. 0.88, <0.001) while it was a poor marker to discriminate between SIAD and TIH (0.65, NS vs. 0.67, NS). In conclusions, FEUA is an excellent marker to discriminate SIAD vs. sodium depleted patients treated with furosemide and/or potassium canrenoate while the diuretic withdrawal, beyond obtaining a serum Na normalization, is still mandatory for differential diagnosis of sodium depleted patients affected by thiazide-induced hyponatraemia.

Highlights

Hyponatraemia is a frequent electrolyte imbalance occurring in up to 25-30% of hospitalized patients where syndrome of inappropriate antidiuresis (SIAD) is the most common etiology present in nearly 35% of hyponatremic inpatients [1, 2]
Our study aimed to investigate the diagnostic role of these alternative markers of volume status, serum uric acid and fractional excretion of uric acid (FEUA), in hyponatraemic patients treated with different diuretic drugs
Our results show that FEUA discriminated better than serum uric acid (sUA) between SIAD and diuretic-induced hyponatremia (DIH) patients while it was a poor marker to discriminate between SIAD and thiazide-induced hyponatremia (TIH) (0.65, NS vs. 0.67, NS)

Summary

Introduction

Hyponatraemia is a frequent electrolyte imbalance occurring in up to 25-30% of hospitalized patients where syndrome of inappropriate antidiuresis (SIAD) is the most common etiology present in nearly 35% of hyponatremic inpatients [1, 2]. The actual guidelines suggest different algorithms to help the physicians in the differential diagnosis of hypotonic hyponatraemia, but a potential bias is coming from the clinical assessment of the volemic status, especially in diuretic-treated patients [3,4,5]. The SIAD diagnosis is complicated in the presence of diuretic therapy due to the misleading clinical assessment of the extracellular volume status [6]. The presence of diuretics arbitrarily excluded the diagnosis of SIAD in hyponatremic patients [7, 8]. In order to make SIAD diagnosis it is often necessary to withdraw diuretic therapy up to 10 days [9]

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