What does the 24-Hour Urine Creatinine test measure?

Why is 24-Hour Urine Creatinine measured?

A 24-hour urine creatinine measurement serves two purposes — it validates the adequacy of the collection itself (low excretion flags an incomplete sample and invalidates other analytes measured in that collection), and it provides a denominator to express spot-urine results as ratios (for instance, albumin-to-creatinine or protein-to-creatinine ratios) when a timed collection is impractical. Clinicians also use the value to estimate creatinine clearance when measured alongside serum creatinine, though eGFR equations have largely supplanted formal clearance for routine GFR estimation.

Reference ranges

Standard reference

Approximately 800–2,000 mg/24 h in men and 600–1,600 mg/24 h in women; dependent on muscle mass, age, and laboratory.

Functional medicine optimal

Expected daily excretion tracks lean body mass: practitioners compare the patient's result against sex- and age-adjusted ranges rather than a single universal threshold, and flag values below approximately 10–15 mg/kg/day as potentially incomplete collections.

Units

mmol/24 h, g/24 h, mg/24 h, mg/d, mmol/d

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