What does the 24-Hour Urine Chloride test measure?

Why is 24-Hour Urine Chloride measured?

Urinary chloride is central to the evaluation of metabolic alkalosis and hyponatraemia. In metabolic alkalosis, a low urine chloride (typically <25 mmol/24 h or <25 mmol/L in a spot sample) indicates chloride-responsive (volume-depleted) causes such as vomiting or diuretic use, while a high urine chloride points to chloride-resistant causes such as primary hyperaldosteronism or severe hypokalaemia. In hyponatraemia, urinary chloride aids the distinction between volume-depleted states (low urine chloride) and syndrome of inappropriate antidiuresis or salt wasting (higher urine chloride). The 24-hour collection integrates day and night variation and dietary intake, making it more reliable than a spot sample when steady-state assessment is needed.

Reference ranges

Standard reference

110–250 mmol/24 h, diet-dependent.

Functional medicine optimal

Optimal excretion mirrors dietary intake; in Western diets this typically falls within 110–250 mmol/24 h. Values outside this range warrant correlation with serum electrolytes, volume status, and the clinical scenario.

Units

mmol/24 h, mEq/24 h

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.