Saline Infusion Test in Hyponatremia

Inclusion Criteria: * Plasma sodium 120-130 mmol/L * Effective osmolality (2 x plasma sodium + plasma glucose) \< 275 milliosmol/L * Age \> 18 years Exclusion Criteria: * Intensive care unit (ICU) admission * Adequate sodium correction rate: \> 4 mmol/L last 24 hours * Primary polydipsia: urine osmolality \< 100 mOsm/L * Hypertonic saline therapy * Adrenal insufficiency * Severe heart failure: ejection fraction \< 35 % or clinical suspicion of decompensated heart failure * Ascites grade 3 (marked abdominal distention and discomfort) * Chronic renal failure stage 4 or 5: estimated glomerular filtration rate \< 30 * Failure to submit informed consent