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Creatinine clearance (24-hour urine)

Measured creatinine clearance from a timed urine collection and serum creatinine

Sources last checked: 2026-11-03

Creatinine clearance (24-hour urine)

Measured creatinine clearance from a timed urine collection and serum creatinine

Creatinine units
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Accuracy depends entirely on a complete collection: discard the first morning void at the start, include the void at the end, and compare total creatinine excretion with what is expected for the patient's muscle mass. Tubular creatinine secretion makes creatinine clearance exceed true GFR, increasingly so as GFR falls.

Source: Rehberg PB. Studies on kidney function: the rate of filtration and reabsorption in the human kidney. Biochem J 1926;20(3):447-460.Open

What is the Creatinine clearance (24-hour urine)?

Measured creatinine clearance compares the creatinine excreted in a timed urine collection with the serum creatinine concentration. The clearance principle for creatinine goes back to Rehberg (1926). It does not depend on age, sex or race coefficients, which makes it useful when estimating equations are unreliable.

When to use it

  • Extremes of muscle mass (amputation, cachexia, paraplegia, bodybuilders) where eGFR is unreliable
  • Unusual diets (vegetarian, creatine supplements) that change creatinine generation
  • Pregnancy and other situations where eGFR equations are not validated
  • When a protocol explicitly asks for measured creatinine clearance

When not to use it

  • Unstable renal function (AKI), where creatinine is not in steady state
  • When the collection is known to be incomplete
  • As a substitute for a measured GFR (iohexol, inulin) when precision really matters

How it is calculated

CrCl (mL/min) = (U_Cr × V) / (S_Cr × t) V in mL, t in minutes (24 h = 1440), U_Cr and S_Cr in the same unit

Clinical pearls and limitations

  • Accuracy depends entirely on a complete collection: discard the first morning void at the start, include the void at the end, and compare total creatinine excretion with what is expected for the patient's muscle mass. Tubular creatinine secretion makes creatinine clearance exceed true GFR, increasingly so as GFR falls.
  • Incomplete collection is the main source of error; check total creatinine excretion against expected values for muscle mass.
  • Creatinine clearance overestimates GFR because of tubular secretion; the overestimate grows as GFR falls.
  • To compare with eGFR, normalise to 1.73 m²: CrCl × 1.73 / BSA.
  • Urine creatinine is usually reported in mmol/L and serum creatinine in µmol/L — mixing them up gives a 1000-fold error, which is why the unit choice is explicit here.

Frequently asked questions

How is creatinine clearance calculated from a 24-hour urine?

(Urine creatinine × urine volume in mL) / (serum creatinine × 1440 min), with urine and serum creatinine in the same unit.

What is a normal creatinine clearance?

In healthy young adults roughly 90–140 mL/min, falling with age; it is higher than true GFR because creatinine is also secreted.

Cockcroft-Gault or 24-hour urine?

Cockcroft-Gault estimates clearance from serum creatinine, age and weight; the 24-hour collection measures it and is preferred when body composition is atypical — if the collection is complete.

How do I collect a 24-hour urine?

Empty the bladder at the start and discard that urine, collect all urine for 24 hours, and include a final void at the end.

Evidence and guidelines

  1. Primary source: Rehberg PB. Studies on kidney function: the rate of filtration and reabsorption in the human kidney. Biochem J 1926;20(3):447-460.

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For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.