Cockcroft-Gault CrCl is the most common formula used to measure creatinine clearance, and approximating glomerular filtration rate (GFR). Although creatinine clearance slightly overestimates the glomerular function by 10-20%, it is considered the standard for drug dosing adjustments.
When calculating for extremes of weights, the Cockcroft-Gault equation seems to become less accurate – underestimates for overweight/obese patients and overestimates for underweight individuals. Hence, adjustments and estimates are made for such cases as follows:
- Underweight (BMI < 18.5): No adjustment. Weight uses TBW.
- Normal Weight (BMI 18.5 - 22.9): Weight uses IBW (with the range using the actual body weight).
- Overweight/Obese (BMI = 23): Weight uses adjusted body weight (with the range using IBW).