Creatinine Clearance (Cockcroft-Gault)

Cockcroft-Gault: estimating creatinine clearance

Published in 1976, the Cockcroft-Gault formula estimates creatinine clearance (ClCr) from three inputs: age, weight, and serum creatinine. The equation is ClCr = [(140 − age) · weight] / (72 · Scr), giving a result in mL/min, and you multiply by 0.85 for women. Take a 50-year-old man weighing 70 kg with Scr of 1.0 mg/dL: ClCr = (90 · 70) / (72 · 1.0) = 87.5 mL/min. One thing to keep in mind is that, unlike eGFR (CKD-EPI), this result is not normalized to a 1.73 m² body surface area. It gives you absolute clearance, which is the number you actually want when dosing drugs.

Applications and context

When the goal is to estimate glomerular filtration, modern guidelines lean toward CKD-EPI (which dropped the race variable in 2021). Cockcroft-Gault, though, is still the reference for drug dose adjustment. You'll see it cited in package inserts (FDA/EMA) for vancomycin, aminoglycosides, DOACs, and renally cleared chemotherapy. It's the default in oncology, geriatrics, and ICU prescribing for older patients. With obese patients, switch to ideal or adjusted body weight so you don't overestimate ClCr.

FAQ

Cockcroft-Gault or CKD-EPI? Reach for CKD-EPI when you're staging or screening CKD. Use Cockcroft-Gault for dose adjustment, since that's the equation behind most drug-label studies.

Which weight in obese patients? Stay away from actual body weight, because it pushes ClCr too high. Go with ideal body weight, or adjusted body weight once BMI is > 30.

Does it work in acute kidney injury? No. The formula assumes creatinine has settled at steady state. During AKI the value is still moving, and no equation gives a reliable ClCr under those conditions.