Creatinine clearance (24-hour urine)

What it measures

Creatinine clearance compares creatinine in a timed urine collection with serum creatinine to measure filtration directly. It is used when eGFR may be unreliable, such as extremes of body size or muscle mass.

Specimen and preparation

• Specimen: 24-hour urine collection plus serum creatinine taken during the collection
• Tube: Urine top
• Preparation: Discard the first morning void, then collect all urine for 24 hours including the next morning's first void; keep refrigerated. Record height and weight.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Pregnancy
• High protein intake
• Early diabetes (hyperfiltration)

Causes of low values

• Kidney disease of any cause
• Incomplete urine collection
• Reduced renal blood flow
• Ageing

Method

Calculated: (urine creatinine × urine volume) ÷ (serum creatinine × time), corrected to 1.73 m²

Good to know

Incomplete collection is the main source of error; check that 24-h urine creatinine matches expected output (about 15–25 mg/kg/day).

Related tests