Creatinine clearance is one of the oldest and most widely cited markers of kidney function. It appears on virtually every drug label that mentions renal dose adjustment — and the Cockcroft-Gault formula, published in 1976, generates it from three routine values: age, body weight, and serum creatinine.
This guide walks through how the formula works, what your number means, when nephrology referral makes sense, and how Cockcroft-Gault relates to modern GFR estimators (CKD-EPI 2021).
What does creatinine clearance measure?
Creatinine is a by-product of muscle metabolism. Its production is fairly constant, and the kidneys eliminate almost all of it. Clearance is the volume of plasma cleared of creatinine per minute — and therefore an indirect measure of how many millilitres of blood your kidneys filter in the same time.
That makes clearance a surrogate marker for the glomerular filtration rate (GFR). A direct measurement requires a 24-hour urine collection or inulin clearance — Cockcroft-Gault gives you a usable estimate from routine labs in seconds.
The Cockcroft-Gault formula
CrCl = (140 − age) × weight (kg) / (72 × SCr mg/dL)
For women: result × 0.85
Using SI units (µmol/L)? The calculator converts automatically: 88.4 µmol/L = 1 mg/dL. The 0.85 correction for women reflects, on average, lower muscle mass; without it, the formula would systematically overestimate clearance in women.
Interpreting your value
| Clearance | Interpretation | CKD stage |
|---|---|---|
| ≥ 90 mL/min | Normal | G1 |
| 60 – 89 | Mildly decreased | G2 |
| 30 – 59 | Moderately decreased | G3 |
| 15 – 29 | Severely decreased | G4 |
| < 15 | Kidney failure | G5 |
CKD stages G3 and below sustained for more than 3 months meet criteria for chronic kidney disease (KDIGO 2024). The lower the value, the more important dose adjustment, avoidance of nephrotoxic drugs, and nephrology co-management become.
Cockcroft-Gault vs. CKD-EPI
KDIGO recommends CKD-EPI 2021 as today's standard for estimating GFR — it is more accurate, especially in normal to mildly decreased function. Cockcroft-Gault still matters: many drug labels and older studies are anchored to it, which is why pharmacists keep using it.
Practical advice: compute both. eGFR helps stage kidney function; creatinine clearance drives concrete drug dosing.
When the formula misleads
- Obesity — body weight in the formula overstates active muscle volume. With BMI > 30, ideal body weight or eGFR is often more honest.
- Sarcopenia / underweight — low muscle mass artificially lowers serum creatinine; clearance can look better than it is.
- Acute kidney injury — the formula assumes a steady state. Rapidly rising creatinine breaks that assumption.
- Pregnancy — physiologically increased GFR. Cockcroft-Gault tends to underestimate.
- Vegan diet — low meat intake lowers serum creatinine and may slightly overestimate clearance.
Related topics & tools
- GFR calculator — modern eGFR via CKD-EPI 2021 complements creatinine clearance. Read the GFR guide.
- Blood pressure — hypertension is the second leading cause of CKD globally. See how to measure blood pressure correctly.
- Diabetes risk — diabetes is the #1 driver of CKD worldwide. Check the FINDRISC score.
Run your Cockcroft-Gault calculation
Anonymous, instant. Supports kg/lbs and mg/dL/µmol/L.
Open the Creatinine Clearance Calculator →Frequently asked questions
How often should I check clearance?
Once a year is enough for stable kidney function without risk factors. With diabetes, hypertension, new nephrotoxic medication, or known CKD G3+, every 3–6 months is reasonable.
My value is 65 mL/min — is that bad?
That falls into CKD stage G2 (mildly decreased). On its own it is not a disease — what matters is the trend, presence of albuminuria, and the underlying cause. Discuss with your primary-care doctor.
Which drugs are nephrotoxic?
Common examples: NSAIDs (ibuprofen, diclofenac), aminoglycosides, contrast media, lithium, high-dose paracetamol, certain antibiotics. With clearance < 60 mL/min, ask your pharmacist or doctor before starting any of them.
Do I need to fast before the blood test?
Not strictly. However, a large meat meal can transiently raise serum creatinine; many labs suggest avoiding meat for the 12 hours before the draw.