Creatinine Clearance (Cockcroft-Gault)

Cockcroft-Gault: creatinine clearance estimate

The Cockcroft-Gault formula (1976) estimates creatinine clearance (ClCr) from three things you already know: age, weight, and serum creatinine. The equation is ClCr = [(140 − age) · weight] / (72 · Scr) in mL/min, with the result cut by a factor of 0.85 for women. Run it for a 60-year-old woman of 70 kg with Scr 1.0 mg/dL and you get ClCr = (80 · 70) / (72 · 1.0) · 0.85 ≈ 66.1 mL/min. Note that this number is not normalized to 1.73 m². It is the absolute clearance, and that is exactly the figure drug dosing studies were built around.

Clinical context

When the goal is to stage or screen for CKD, current guidelines lean toward CKD-EPI (race-free since 2021). Cockcroft-Gault holds its ground in a different setting: drug dose adjustment. It is the formula written into FDA and EMA labels for vancomycin, aminoglycosides, DOACs, and chemotherapy cleared by the kidneys, and it is routine when prescribing for geriatric patients, in oncology, and for older patients in the ICU. One caveat: in obesity (BMI > 30), reach for ideal or adjusted body weight, otherwise the formula overshoots ClCr.

FAQ

Cockcroft-Gault or CKD-EPI? Use CKD-EPI to stage CKD. Use Cockcroft-Gault to adjust drug doses, since that is what most label studies relied on.

Which weight in obese patients? Plug in actual body weight and ClCr comes out too high. Go with ideal body weight, or adjusted body weight once BMI passes 30.

Does it work in acute kidney injury? No. It assumes creatinine has reached steady state. During AKI the creatinine is still moving, and no equation pins down ClCr reliably under those conditions.