Question 1

What is creatinine clearance used for?

Accepted Answer

Creatinine clearance approximates how much blood the kidneys clear of creatinine per minute. It’s the estimate most commonly referenced in drug labeling for renal dose adjustments, so it’s widely used by pharmacists and prescribers when dosing renally cleared medications.

Question 2

How is this different from eGFR?

Accepted Answer

Both estimate kidney function from serum creatinine, but they use different equations derived from different populations. Cockcroft-Gault (used here) factors in body weight directly and was derived from a smaller, older cohort; eGFR (CKD-EPI) is the modern standard for staging chronic kidney disease. Drug labels typically specify which one they were validated against — usually Cockcroft-Gault.

Question 3

Should I use actual, ideal, or adjusted body weight?

Accepted Answer

The original Cockcroft-Gault study used actual body weight. In practice, many clinicians use ideal body weight for underweight patients and an adjusted body weight for obese patients, since actual weight can overestimate clearance in those cases. Which weight to use depends on the specific drug and clinical situation — ask a pharmacist if you’re unsure.

Question 4

Why does sex affect the result?

Accepted Answer

The equation multiplies the result by 0.85 for female patients, reflecting that women have less muscle mass on average and therefore lower creatinine production for a given kidney function.

Question 5

Is this calculator accurate for elderly or very obese patients?

Accepted Answer

Cockcroft-Gault can be less accurate at the extremes of age, muscle mass, and body weight. It also wasn’t derived using standardized creatinine assays used today, which can introduce systematic differences. Clinical judgment and, where needed, a measured clearance remain important in these cases.

Creatinine Clearance Calculator

How creatinine clearance is calculated

Cockcroft-Gault (1976)

Common questions