Calculation

Creatinine clearance = (UV / P) ml per minute, where:

• concentration of creatinine in urine = U
• concentration of creatinine in plasma = P
• volume of urine collected in T minutes = V

This formula shows SI units.

• UV Amount of creatinine in 24h of urine is reported by the lab in mmol/24h; multiply by 1000 to convert to micromols
• P Serum creatinine is reported in micromols/l; multiply by 1000 to do calculation for mls
• 1440 Number of minutes in 24h CrCl(mls per min) = UVx1000x1000/(Px1440)

Alternatively, if urinary collection is difficult, the Cockcroft-Gault equation aims to predict creatinine clearance from knowledge of serum creatinine, age and weight:

• creatinine clearance = (((140 - age in years) x (wt in kg)) x 1.23) / (serum creatinine in micromol/l)

For women multiply the result of calculation by 0.85.

The second calculation is unreliable if the patient has unstable renal function, is very obese, or is oedematous.

Reference:

1. Cockcroft D (1976). Nephron, 16, 31.