Formula & Calculator
Creatinine Clearance (Cockcroft-Gault)
Estimates kidney filtering function from age, weight, and a routine blood test (serum creatinine).
Interpretation
CrCl = ((140−age)×mass) / (72×Scr) × 0.85 (if female). Estimates glomerular filtration rate from serum creatinine. Used to adjust drug dosing and assess renal function.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| CrCl | Creatinine clearance | mL/min |
| age | Age | years |
| mass | Body mass | kg |
| Scr | Serum creatinine | mg/dL |
What it means
The Cockcroft‑Gault equation estimates creatinine clearance (CrCl), a proxy for glomerular filtration rate (GFR), using age, weight, and serum creatinine (Scr). It is widely used to adjust drug doses for patients with renal impairment. It accounts for muscle mass through weight and age. The formula gives a value in mL/min. A correction factor of 0.85 is applied for females due to lower muscle mass. It is used in clinical pharmacology and nephrology. While more accurate equations exist (e.g., MDRD, CKD‑EPI), it remains common for drug dosing. Understanding this equation is essential for safe prescribing and for monitoring kidney function.
Worked example
Creatinine Clearance (Cockcroft‑Gault) – Two Detailed Examples
Real‑World| Parameter | Value |
|---|---|
| age (yr) | 40 |
| mass (kg) | 70 |
| Scr (mg/dL) | 1.0 |
| Parameter | Value |
|---|---|
| age | 60 |
| mass | 80 |
| Scr | 1.2 |
Common mistakes
- Cockcroft‑Gault: CrCl = ((140 − age) × mass) / (72 × Scr) – then ×0.85 for women.
- Age: In years.
- Mass: In kilograms – use actual body weight.
- Scr: Serum creatinine in mg/dL – not µmol/L.
- Result: Creatinine clearance in mL/min – an estimate of GFR.
- Limitations: May overestimate in obese patients and underestimate in malnourished.
Applications
The Cockcroft‑Gault formula estimates creatinine clearance (CrCl), a measure of kidney function, based on age, weight, serum creatinine, and sex. It is widely used to adjust drug dosing for patients with renal impairment, especially for medications that are cleared by the kidneys. Clinicians and pharmacists use CrCl to determine safe and effective doses, to monitor kidney disease progression, and to assess the need for dialysis. This formula is essential in geriatrics, oncology, and critical care. By calculating CrCl, healthcare providers can avoid drug toxicity and optimise therapy. Understanding renal function is critical for safe prescribing and patient safety.
- Drug dose adjustment for renally excreted medications
- Assessment of kidney function in chronic kidney disease
- Monitoring of drug side effects and toxicity
- Clinical research and pharmacovigilance
- Geriatric and critical care medicine
Frequently Asked Questions
It estimates kidney function (glomerular filtration rate) from age, weight, and serum creatinine: CrCl = ((140−age) × mass(kg)) / (72 × Scr), with ×0.85 for women.
age = years
mass = actual body weight (kg)
Scr = serum creatinine (mg/dL)
72 is a constant derived from population data.
It is used to adjust drug dosages in patients with renal impairment to avoid toxicity. It is also a marker of renal function.
Women have, on average, lower muscle mass, so their creatinine clearance is lower for the same serum creatinine. The correction accounts for this.
A 60‑year‑old man, weight 80 kg, Scr = 1.2 mg/dL. CrCl = ((140−60)×80)/(72×1.2) = (80×80)/86.4 = 6400/86.4 ≈ 74.1 mL/min.
- It overestimates kidney function in obese patients (because creatinine clearance is based on actual weight, but lean body mass is more appropriate).
- It is less accurate at extremes of age and weight.
- It is not validated for use with the new, standardised creatinine assays.
- Forgetting the 0.85 correction for women, which overestimates CrCl and can lead to incorrect dosing.
- Using the formula for patients with unstable renal function.
- Using Scr in µmol/L without converting (divide by 88.4 to get mg/dL).
The MDRD and CKD‑EPI are based on serum creatinine and other factors, and are more accurate for estimating GFR. Cockcroft‑Gault is still used for drug dosing.
CrCl is an estimate of creatinine clearance, which approximates GFR but may overestimate it because creatinine is both filtered and secreted.
To express CrCl per 1.73 m², multiply by 1.73 / BSA (using Mosteller or Du Bois).