Urine electrolytes assays are typically employed to resolve in-patient hyponatraemia diagnoses. A urinary sodium <20 mmol/L is consistent with a dehydrated patient with functional renal tubules who will respond to rehydration, while a urinary sodium >20 mmol/L (typically >50 mmol/L), in conjunction with a low/normal urea and/or urate, may be indicative of SIADH.
|No reference range|
Random urine (preferred) or 24 hour urine collection
Random urine: 0.5 mL
or 24 hour urine collection
Random urine: 1 day
24 hour urine collection: 2 days