Cockcroft-Gault vs. eGFR
It is important to distinguish between Staging and Dosing when evaluating kidney function:
eGFR (MDRD / CKD-EPI)
Used to diagnose and stage Chronic Kidney Disease (Stages 1-5). It is normalized to body surface area (1.73 m²).
CrCl (Cockcroft-Gault)
Used by the FDA to determine drug dosages. Most package inserts (e.g., antibiotics, NOACs) base their safety data on this formula.
Which Weight Should I Use?
The choice of weight in the equation significantly alters the result. Clinical consensus generally suggests:
- Normal Weight:Use Actual Body Weight. This is the most accurate reflection of muscle mass for standard patients.
- Obese (BMI > 30):Use Adjusted Body Weight (ABW). Adipose tissue (fat) does not produce creatinine. Using the total actual weight would overestimate clearance and risk overdose.
- Underweight:Use Actual Body Weight. Using Ideal Body Weight would assume more muscle mass than the patient actually has, ignoring their frailty.
Frequently Asked Questions
Why do we still use Cockcroft-Gault?
Despite being developed in 1976, the Cockcroft-Gault equation remains the standard because almost all historical drug safety trials used it to establish dosing guidelines. Modern formulas like CKD-EPI are more accurate for staging disease, but using them for dosing might lead to errors if the drug's package insert specifies CrCl.
When should I use Adjusted Body Weight?
Adjusted Body Weight (ABW) is typically used when a patient's actual weight is more than 20-30% above their Ideal Body Weight (IBW). Creatinine production is linked to muscle mass, not fat. Using the massive actual weight of an obese patient would falsely inflate their clearance rate, potentially leading to a toxic drug overdose.
What is a normal Creatinine Clearance?
For a healthy young male, a normal CrCl is approximately 97 to 137 mL/min. For women, it is 88 to 128 mL/min. This number naturally declines with age (roughly 1 mL/min per year after age 40), so an 80-year-old with a CrCl of 60 might actually be considered "normal for age."
Does muscle mass affect this result?
Yes, significantly. Since creatinine is a waste product of muscle breakdown, patients with very low muscle mass (sarcopenia, amputation, or elderly) may have low serum creatinine. This formula might overestimate their kidney function because it assumes a standard amount of muscle. In these cases, a 24-hour urine collection is more accurate.
Can I use this for children?
No. The Cockcroft-Gault equation is strictly for adults (age 18+). For pediatric patients, the Schwartz Equation (which uses height and a constant k) is the standard method for estimating glomerular filtration rate.
References
- National Kidney Foundation. Cockcroft-Gault Formula.
- GlobalRPH. Creatinine Clearance Multi-Weight Calculator.
- FDA. Guidance on Renal Impairment Dosing.
- UpToDate. Assessment of Kidney Function.
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: January 2026.