Creatinine Clearance (Cockcroft-Gault)
Estimates creatinine clearance for renal function assessment and contrast/renal drug dosing.
The Cockcroft-Gault equation estimates creatinine clearance (a surrogate for glomerular filtration rate) from age, weight, serum creatinine and sex. It remains widely used for renal drug dosing and for assessing risk before iodinated contrast administration.
📐 Formula
CrCl = ((140 − age) × weight) / (72 × Scr) × (0.85 if female)
🎯 When to Use
- Screening renal function before iodinated contrast to weigh nephrotoxicity risk.
- Adjusting renally-cleared drug doses.
- Bedside estimate when a measured clearance is unavailable.
⚙️ How It Works
- Subtract age from 140 and multiply by body weight in kilograms.
- Divide by 72 times the serum creatinine in mg/dL.
- Multiply by 0.85 for female patients to correct for lower muscle mass.
- Result is estimated creatinine clearance in mL/min.
📊 Interpreting the Result
- ≥60 mL/min: generally adequate renal function.
- 30-59 mL/min: moderate impairment; use caution with nephrotoxic contrast and adjust dosing.
- <30 mL/min: severe impairment; high caution with iodinated contrast and careful risk-benefit assessment.
⚠️ Limitations & Pitfalls
- Assumes stable creatinine; unreliable in acute kidney injury.
- Overestimates clearance in oedematous or obese patients (actual weight); ideal or adjusted weight may be preferable.
- Not indexed to body surface area; differs from CKD-EPI/MDRD eGFR.
📚 References
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.