— mL/min

Creatinine Clearance Calculator (Cockcroft–Gault)

The Cockcroft–Gault (CrCl) formula estimates creatinine clearance — an approximation of renal function used commonly for drug dosing and some clinical decisions. It uses age, body weight, sex, and serum creatinine to estimate how many millilitres of plasma are cleared of creatinine per minute (mL/min). Note: for CKD staging and standardized reporting, modern equations such as CKD-EPI eGFR (mL/min/1.73 m²) are preferred; Cockcroft–Gault remains useful for drug-dosing where many pharmacokinetic studies used CrCl.

Why Use Cockcroft–Gault

• Drug dosing: Many medication dosing recommendations (especially older antibiotics, anticoagulants, and chemotherapy agents) are based on CrCl.
• Quick bedside estimate: Requires only age, weight, sex, and serum creatinine (no laboratory normalization needed).
• Clinical context: Useful when body size is relevant to clearance (weight is included in the formula).

Key Parameters

• Age (years)
• Body weight (kg) — actual body weight (ABW), ideal body weight (IBW), or adjusted body weight (AdjBW) as clinically appropriate
• Serum creatinine (Scr) — mg/dL or µmol/L (see unit conversion below)
• Sex (male / female) — female values are multiplied by 0.85

Formula (Traditional)

CrCl (mL/min) =   (140 − age) × weight (kg)
         ———————————————
         72 × serum creatinine (mg/dL)

For females: multiply the result by 0.85 (i.e., CrCl_female = CrCl_male × 0.85).

Unit Conversion (Serum Creatinine)

If serum creatinine is reported in µmol/L, convert to mg/dL before using the formula:
Serum creatinine (mg/dL) = Serum creatinine (µmol/L) ÷ 88.4

Which Weight to Use?

• Non-obese adults: Use actual body weight (ABW).
• Obese patients (BMI ≥30 kg/m²): many clinicians use Ideal Body Weight (IBW) or Adjusted Body Weight (AdjBW) to avoid overestimating CrCl.
• IBW (Devine formula):
  Male IBW (kg) = 50 + 2.3 × (height in inches − 60)
  Female IBW (kg) = 45.5 + 2.3 × (height in inches − 60)
• AdjBW: AdjBW = IBW + 0.4 × (ABW − IBW) — sometimes used when ABW greatly exceeds IBW.
• Document which weight you used; many dosing guidelines specify the weight type.

Step-by-Step Example

Problem: Estimate creatinine clearance for a 65-year-old male, weight 70 kg, serum creatinine 1.2 mg/dL.

Step 1 — Inputs:
Age = 65 years; Weight = 70 kg (ABW); Serum creatinine = 1.2 mg/dL; Sex = male.

Step 2 — Apply formula:
Numerator = (140 − 65) × 70 = 75 × 70 = 5,250
Denominator = 72 × 1.2 = 86.4

Step 3 — Calculate CrCl:
CrCl = 5,250 ÷ 86.4 = 60.8 mL/min (rounded)

If female: multiply by 0.85 → e.g., female with identical inputs → 60.8 × 0.85 ≈ 51.7 mL/min.

How the Calculator Works (User Flow)

1. Enter age, sex, weight, and serum creatinine (choose mg/dL or µmol/L).
2. Select which weight to use (Actual, Ideal, or Adjusted) — provide height if IBW/AdjBW chosen.
3. Click “Calculate” — the tool converts units (if required), applies the Cockcroft–Gault formula, and displays CrCl in mL/min.
4. Optional: show drug-dosing bands or recommendations (based on commonly used dosing thresholds) as guidance only.

Interpretation & Common Uses

• CrCl > 60 mL/min: generally adequate renal function for most drug dosages (verify drug-specific guidance).
• CrCl 30–60 mL/min: moderate impairment; many drugs require dose reduction or extended dosing interval.
• CrCl < 30 mL/min: severe impairment; many medications need major dose adjustment or avoidance.
• Always check the specific drug monograph or clinical guideline for recommended dosing in renal impairment.

Limitations & Important Considerations

• Cockcroft–Gault estimates creatinine clearance, not standardized eGFR; values are not directly comparable to eGFR reported as mL/min/1.73 m² without adjustment for body surface area (BSA).
• In acute kidney injury (rapidly changing creatinine), the formula is unreliable — it assumes steady-state creatinine production and excretion.
• In extremes of muscle mass (very low or very high), serum creatinine may not reflect true GFR; interpret cautiously.
• For chronic kidney disease staging and many clinical decisions, CKD-EPI eGFR (mL/min/1.73 m²) is preferred; however, drug dosing often still references Cockcroft–Gault.
• Document the units and weight method used when reporting CrCl for dosing decisions.

FAQs – Cockcroft–Gault Creatinine Clearance

1. Should I use Cockcroft–Gault or eGFR for drug dosing?
Many drug dosing guidelines were developed using Cockcroft–Gault. When a drug’s dosing recommendation explicitly references CrCl, use Cockcroft–Gault (and the weight method specified). If guidance refers to eGFR or provides both, follow the drug-specific recommendation.

2. How do I convert CrCl (mL/min) to eGFR (mL/min/1.73 m²)?
Convert CrCl to a BSA-standardized value by indexing to body surface area (BSA):
eGFR_indexed = (CrCl × 1.73) / BSA
where BSA (m²) can be calculated using Mosteller or other BSA formulas. Note differences between CrCl and eGFR persist due to methodologic differences.

3. What do I do for obese patients?
Consider using IBW or AdjBW to avoid overestimation of kidney function when ABW is much greater than IBW. Check local practice or drug monographs for preferred approach.

4. Is the female correction (×0.85) evidence-based?
The 0.85 multiplier reflects lower average muscle mass and creatinine generation in females; it is an established part of the Cockcroft–Gault equation.

5. Can children use Cockcroft–Gault?
No — pediatric-specific formulas (for example, the Schwartz equation) should be used for children.

6. How should I handle very low serum creatinine values?
Very low Scr (e.g., <0.6 mg/dL) in frail or elderly patients may overestimate CrCl; interpret in clinical context and consider alternative measures (24-hour urine collection or cystatin C-based estimates) when critical.

7. Is a 24-hour urine collection better?
A 24-hour urine creatinine clearance can provide a measured CrCl but is inconvenient and subject to collection errors. It may be used when precise measured clearance is required.

8. Does muscle mass change the result?
Yes. Serum creatinine depends on muscle mass; unusually high or low muscle mass can skew the estimate away from true GFR.

9. When should I re-check CrCl?
Re-check when serum creatinine changes, when dosing high-risk medications, or during acute illness that may affect renal function.

10. Is this calculator medical advice?
No. This tool provides an estimate for clinical decision support. Always combine estimates with clinical judgment and consult drug-specific dosing guidelines and treating clinicians when making therapeutic choices.

Quick Disclaimer

The Cockcroft–Gault calculator provides an estimated creatinine clearance for informational and clinical support purposes. It does not replace clinical judgment, measured renal function tests, or institutional dosing protocols. For patients with unstable renal function, unusual body composition, or critical dosing decisions, consult nephrology or pharmacy and consider measured clearance methods.