What Is Creatinine Clearance?
Creatinine is a waste product produced at a roughly constant rate by muscle metabolism. Healthy kidneys continuously filter it out of the blood. When kidney function declines, creatinine accumulates — so a higher serum creatinine generally means lower kidney clearance.
Creatinine clearance (CrCl) expresses how much blood the kidneys filter per minute, in mL/min. It is one of the primary clinical measures of kidney function and is used to:
- Classify chronic kidney disease (CKD) stage
- Adjust drug doses for renally cleared medications
- Detect acute kidney injury
Cockcroft-Gault Equation
Published in 1976 by Cockcroft and Gault, this formula remains the standard for drug dosing because most pharmacokinetic studies used it:
CrCl = [(140 − Age) × Weight × Sex factor] ÷ (72 × Serum Creatinine)
Where weight is in kg, serum creatinine is in mg/dL, and the sex factor is 1.0 for men and 0.85 for women.
Weight Used in This Calculator
The original equation used actual body weight, but obese patients produce relatively less creatinine per kg of body weight, causing overestimation. This calculator selects the weight automatically:
| Patient | Weight used |
|---|---|
| ABW ≤ IBW (underweight or lean) | Actual Body Weight (ABW) |
| IBW < ABW ≤ 1.3 × IBW (normal–overweight) | Actual Body Weight (ABW) |
| ABW > 1.3 × IBW (obese) | Adjusted Body Weight: IBW + 0.4 × (ABW − IBW) |
Ideal Body Weight (Devine formula):
- Men: IBW = 50 + 2.3 × (height in inches − 60)
- Women: IBW = 45.5 + 2.3 × (height in inches − 60)
CKD-EPI 2021
The Chronic Kidney Disease Epidemiology Collaboration equation (2021 revision) is the current standard for CKD classification. The 2021 update removed the race coefficient from the 2009 version:
- More accurate than Cockcroft-Gault for classifying kidney disease in the general population
- Reports eGFR normalized to 1.73 m² body surface area (mL/min/1.73 m²)
- Does not use weight — relies on age, sex, and serum creatinine only
CKD Stages
The KDIGO (Kidney Disease: Improving Global Outcomes) 2012 guidelines classify CKD by eGFR:
| Stage | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high |
| G2 | 60 – 89 | Mildly decreased |
| G3a | 45 – 59 | Mild to moderately decreased |
| G3b | 30 – 44 | Moderately to severely decreased |
| G4 | 15 – 29 | Severely decreased |
| G5 | < 15 | Kidney failure |
Note: eGFR alone does not diagnose CKD — the KDIGO definition also requires evidence of kidney damage (e.g. proteinuria, haematuria, structural abnormality) persisting for more than 3 months.
Limitations
- Stable renal function only. Both equations assume creatinine has reached steady state. They are unreliable during acute kidney injury or rapid changes in kidney function.
- Muscle mass. Creatinine is a product of muscle metabolism. Low muscle mass (elderly, malnutrition, amputation) underestimates true creatinine production, causing overestimation of kidney function. High muscle mass (bodybuilders) has the opposite effect.
- Diet. High meat intake temporarily raises serum creatinine; vegetarian diets lower it.
- Extremes of body size. Both equations are less accurate in very obese or very cachectic patients.
- Cystatin C. For patients where accuracy is critical (e.g. before nephrotoxic chemotherapy), cystatin C-based or combined creatinine + cystatin C equations are more reliable.
Sources
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41.
- Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385:1737–1749.
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2013;3(1):1–150.
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.