Validation of New Diagnostic Indices to Simplify Hyponatremia Therapy Assessment in Patients on Thiazide Diuretics

Inclusion Criteria: * Hospitalized patients presenting at University Hospital Basel * aged 18 years or older * able to give informed consent as documented by signature * with serum sodium level \< 133 mmol/l and serum osmolality \< 300 mOsm/kg * with treatment with thiazide or thiazide-like diuretic Exclusion Criteria: * symptomatic hyponatremia in need of 3% hypertonic solution or intensive care treatment * inability or contraindications to undergo the trial (i.e., any acute severe cardiovascular event requiring an immediate intervention) * decompensated liver cirrhosis CHILD C * decompensated heart failure NYHA III or higher * severe valve impairment * untreated adrenal insufficiency * severe kidney disease in need of dialysis * pregnancy or breastfeeding * end of life care * inability to follow the study procedures (i.e., language problem, dementia or critical illness).