CalcCreatinine Clearance (Cockcroft-Gault)
Estimate glomerular filtration rate using the Cockcroft-Gault formula.
Creatinine Clearance Calculator: Assess Kidney Function
Creatinine clearance (CrCl) estimated by the Cockcroft-Gault equation is a widely used clinical tool for assessing kidney function and guiding medication dosing adjustments. By combining age, weight, sex, and serum creatinine levels, this formula provides a practical estimate of glomerular filtration rate without requiring 24-hour urine collection.
Cockcroft-Gault Creatinine Clearance Formula
CrCl (mL/min) = ((140 − Age) × Weight (kg) × (0.85 if female)) / (72 × Serum Creatinine (mg/dL))
The formula multiplies the difference between 140 and your age by your body weight in kilograms. For women, the result is multiplied by a correction factor of 0.85 to account for generally lower muscle mass. This product is then divided by 72 times your serum creatinine level. For example, a 65-year-old man weighing 78 kg with a serum creatinine of 1.2 mg/dL: CrCl = ((140 − 65) × 78) / (72 × 1.2) = (75 × 78) / 86.4 = 5850 / 86.4 = 67.7 mL/min.
Worked Examples
Example 1: Elderly Female Patient
A 72-year-old woman weighing 60 kg has a serum creatinine of 1.0 mg/dL.
CrCl = ((140 − 72) × 60 × 0.85) / (72 × 1.0) = (68 × 60 × 0.85) / 72 = 3468 / 72 = 48.2 mL/min
This CrCl of 48.2 mL/min indicates moderate renal impairment (Stage 3a CKD). Medications cleared by the kidneys would require dose adjustments. For instance, metformin may need reduction and certain antibiotics would require extended dosing intervals.
Example 2: Young Male Patient
A 30-year-old man weighing 85 kg has a serum creatinine of 0.9 mg/dL.
CrCl = ((140 − 30) × 85) / (72 × 0.9) = (110 × 85) / 64.8 = 9350 / 64.8 = 144.3 mL/min
This CrCl of 144.3 mL/min falls within the normal range for a young healthy male (normal: 90–140 mL/min, with slight variation). No medication dose adjustments would be needed based on renal function. The higher value reflects greater muscle mass and younger age.
Common Uses
- Adjusting doses of renally eliminated medications including antibiotics, antivirals, and chemotherapy agents
- Staging chronic kidney disease (CKD) to guide clinical management and referral decisions
- Monitoring kidney function decline over time in patients with diabetes or hypertension
- Determining eligibility for contrast imaging procedures that carry nephrotoxicity risk
- Calculating drug clearance for clinical pharmacokinetic studies and therapeutic drug monitoring
- Screening for renal impairment in pre-operative assessments before major surgery
Common Mistakes
- Using total body weight for obese patients instead of ideal or adjusted body weight, which overestimates CrCl significantly
- Forgetting to apply the 0.85 female correction factor, leading to overestimation of kidney function in women by approximately 15%
- Applying the formula to patients with rapidly changing creatinine levels (acute kidney injury), when steady-state conditions are required
- Using creatinine values in µmol/L without converting to mg/dL (divide µmol/L by 88.4), which produces dramatically incorrect results
Pro Tip
For obese patients (BMI ≥ 30), use adjusted body weight instead of total body weight: AdjBW = IBW + 0.4 × (TBW − IBW). This prevents overestimation of CrCl that occurs because excess adipose tissue does not contribute proportionally to creatinine production. Additionally, always verify the units of serum creatinine — many international labs report in µmol/L while the Cockcroft-Gault formula requires mg/dL. A creatinine of 100 µmol/L equals 1.13 mg/dL, and using 100 directly would yield a CrCl roughly 100 times too low.
Frequently Asked Questions
Cockcroft-Gault remains the standard for medication dosing adjustments per FDA labeling. MDRD and CKD-EPI are preferred for CKD staging and epidemiological studies. For clinical drug dosing decisions, Cockcroft-Gault is still the most widely referenced equation in pharmaceutical prescribing information.
Normal CrCl ranges from 90–140 mL/min for men and 80–125 mL/min for women. Values of 60–89 mL/min indicate mildly reduced function, 30–59 mL/min indicate moderate impairment (Stage 3), 15–29 mL/min indicate severe impairment (Stage 4), and below 15 mL/min indicate kidney failure (Stage 5).
Women generally have less skeletal muscle mass than men of the same weight, resulting in lower creatinine production. Since serum creatinine reflects both creatinine production (from muscle) and kidney clearance, the 0.85 factor adjusts for this physiological difference to provide a more accurate estimate of true GFR in women.
Cockcroft-Gault estimates CrCl within ±20% of measured values in approximately 70–80% of patients. It is less accurate in extremes of age, body composition, muscle mass, and diet. For precise GFR measurement, inulin clearance or iothalamate clearance studies are the gold standard but are rarely used in routine clinical practice.