Creatinine Clearance (Cockcroft-Gault)
Reference for the Cockcroft-Gault formula: CrCl = [(140 - age) × weight / (72 × creatinine)] × 0.85 for women.
Returns CrCl for CKD staging and dosing.
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The Formula
CrCl = [(140 - age) × weight] / (72 × S_Cr) (× 0.85 for women)
The Cockcroft-Gault equation estimates how well the kidneys filter waste from the blood. It is widely used to adjust medication doses in patients with impaired kidney function.
Variables
| Symbol | Meaning |
|---|---|
| CrCl | Creatinine clearance (mL/min) |
| age | Patient's age (years) |
| weight | Patient's weight (kg). Divide lbs by 2.205. |
| S_Cr | Serum creatinine level (mg/dL) |
| 0.85 | Correction factor for women (lower muscle mass) |
Example 1
A 60-year-old man, 80 kg, serum creatinine 1.2 mg/dL
CrCl = [(140 - 60) × 80] / (72 × 1.2)
CrCl = (80 × 80) / 86.4 = 6400 / 86.4
CrCl ≈ 74.1 mL/min (mildly reduced kidney function)
Example 2
A 45-year-old woman, 65 kg, serum creatinine 0.9 mg/dL
CrCl = [(140 - 45) × 65] / (72 × 0.9) × 0.85
CrCl = (95 × 65) / 64.8 × 0.85 = 6175 / 64.8 × 0.85
CrCl ≈ 80.9 mL/min (normal kidney function)
When to Use It
Use the creatinine clearance formula when:
- Adjusting medication doses for patients with kidney impairment
- Screening for chronic kidney disease
- Monitoring kidney function over time
- Assessing eligibility for certain medical procedures
Key Notes
- CKD staging thresholds: ≥ 90 mL/min = Stage 1 (normal/high), 60–89 = Stage 2 (mildly reduced), 30–59 = Stage 3 (moderately reduced), 15–29 = Stage 4 (severely reduced), < 15 = Stage 5 (kidney failure requiring dialysis)
- For obese patients, use Ideal Body Weight (IBW), not actual weight — the formula overestimates CrCl in obesity because adipose tissue generates little creatinine; IBW + 0.4 × (actual − IBW) is the adjusted body weight formula when actual weight exceeds IBW by more than 30%
- A "normal" serum creatinine does not guarantee normal kidney function — frail elderly or malnourished patients produce little creatinine due to low muscle mass; their creatinine of 0.8 mg/dL may correspond to a CrCl of only 30 mL/min
- The CKD-EPI equation (2009) is preferred over Cockcroft-Gault for classifying CKD in modern guidelines, but Cockcroft-Gault remains the standard in most drug prescribing information for dose adjustment recommendations