How to Calculate Creatinine Clearance
The Cockcroft-Gault formula is the recommended method for calculating creatinine clearance: CrCl (mL/min) = [(140 - age) × weight (kg) × 0.85 (if female)] / [72 × serum creatinine (mg/dL)] 1, 2.
Cockcroft-Gault Formula Components
- The formula was originally derived from a dataset of 249 men aged 18-92 years 3
- For females, multiply the result by 0.85 to account for lower muscle mass 1, 2
- To convert serum creatinine from μmol/L to mg/dL, divide by 88.4 1
- Age is measured in years, weight in kilograms, and serum creatinine in mg/dL 1, 2
Weight Considerations
- For patients of normal weight, ideal body weight provides unbiased results 4
- For underweight patients, actual body weight yields the most accurate results 4
- For overweight, obese, and morbidly obese patients, adjusted body weight using a factor of 0.4 (ABW₀.₄) is recommended for the least biased and most accurate calculations 4
- The European Heart Rhythm Association recommends using the mean value between actual and ideal body weight for obese patients 5
Special Populations and Considerations
- The formula tends to be less accurate in elderly patients 1
- In patients with significantly impaired renal function, the formula may overestimate GFR 1
- For pregnant women with renal disease, the Cockcroft-Gault formula using pre-pregnancy weights correlates well with 24-hour creatinine clearance measurements 6
- The formula may underestimate creatinine clearance in women, with some studies suggesting the 0.85 correction factor may be insufficient 7
Clinical Applications
- The American College of Clinical Pharmacy recommends using the Cockcroft-Gault equation for drug dosing 2
- Decreased renal function as calculated by creatinine clearance is an independent predictor of mortality in patients with multi-vessel coronary artery disease 8
- Online calculators are available at various websites including www.kidney.org/professionals/kdoqi/gfr_calculator and www.mdcalc.com/creatinine-clearance-cockcroft-gault-equation 5
- Popular mobile applications for calculating creatinine clearance include NephroCalc, MedMath, MedCalc, Calculate by QxMD, and Archimedes 5
Limitations
- Creatinine clearance provides only a crude measure of renal function and tends to overestimate true GFR because creatinine is both filtered and secreted by the kidneys 1
- The Jaffe method may overestimate serum creatinine by 5-15% compared to enzymatic methods 1
- As renal function declines, tubular secretion and extrarenal elimination of creatinine increase, exaggerating the discrepancy between creatinine clearance and actual GFR 1