Creatinine Clearance Calculator (Cockcroft-Gault)

About the Creatinine Clearance Calculator (Cockcroft-Gault)

The Cockcroft–Gault equation estimates creatinine clearance — how many millilitres of blood the kidneys clear of creatinine each minute — from age, weight, sex and a blood creatinine result. It has long been used in drug labels and pharmacy references, so the number still appears on many reports and in many protocols.

This calculator gives the clearance with the actual body weight and, when you add a height, with the ideal body weight (Devine) and the adjusted body weight used by some protocols for people above their ideal weight. Beside it you see the CKD-EPI eGFR, the standard estimate of kidney function today, so you can see how the two differ. Creatinine can be entered in mg/dL or µmol/L. Nothing you enter leaves your browser.

Reference only: the result must not be used to choose or change medicine doses. Dosing is decided by the prescriber or pharmacist with the drug’s own instructions.

Without a pass, the free preview shows the clearance with actual body weight in full, with what it means, every caution and the first rows of each table; a Pro pass unlocks the ideal- and adjusted-weight results, the eGFR comparison and Copy result.

Common uses

• Checking a creatinine clearance quoted on a report or in a drug reference against the inputs.
• Seeing how much the choice of body weight changes a Cockcroft–Gault result.
• Comparing creatinine clearance with the CKD-EPI eGFR for the same blood test.
• Teaching students the difference between creatinine clearance and eGFR.

The equations

• Cockcroft–Gault: creatinine clearance (mL/min) = (140 − age) × weight (kg) ÷ (72 × serum creatinine (mg/dL)), multiplied by 0.85 for women. Creatinine in µmol/L is divided by 88.4 first.
• Ideal body weight (Devine): men 50 kg, women 45.5 kg, plus 2.3 kg for every inch of height above 5 ft (152.4 cm).
• Adjusted body weight: ideal weight + 0.4 × (actual weight − ideal weight), shown when the actual weight is above the ideal weight.
• CKD-EPI 2021 creatinine eGFR: 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age, × 1.012 for women, with κ = 0.7 (women) or 0.9 (men) and α = −0.241 (women) or −0.302 (men).
• eGFR for your body size: eGFR × body surface area ÷ 1.73, with the Du Bois surface area 0.007184 × weight^0.425 × height^0.725 (kg, cm).

Creatinine clearance is not eGFR

Cockcroft–Gault estimates creatinine clearance in mL/min for the person’s own body. The CKD-EPI equation estimates the glomerular filtration rate per 1.73 m² of body surface, the unit kidney disease is staged in. They measure different things:

• creatinine is also secreted by the kidney tubules, so creatinine clearance runs higher than the filtration rate itself;
• Cockcroft–Gault was developed in 249 men, and the 15% reduction for women was estimated rather than measured;
• it was developed before creatinine assays were standardised, and with today’s standardised (IDMS) creatinine it gives higher values than in the older studies that used it.

The National Kidney Foundation recommends moving away from Cockcroft–Gault for adult medication decisions in favour of eGFR equations scaled to the person’s body surface area, and notes that the FDA now favours eGFR for kidney function in pharmacokinetic studies.

When the estimate can be wrong

• Changing kidney function: after acute kidney injury or any time creatinine is not stable, every creatinine equation lags behind reality.
• Unusual muscle mass: frailty, amputation, paralysis or very high muscle mass change creatinine without any change in the kidneys.
• Body size: with obesity the result depends strongly on which weight is used, and practice differs — the National Kidney Foundation notes that this inconsistency reduces accuracy.
• Older age with low creatinine: some practices raise a creatinine that is below the normal range before using the equation; the National Kidney Foundation notes clear evidence against that adjustment, so this calculator uses the value entered.
• Children and pregnancy: the equation is for adults; pregnancy changes kidney function and body weight.

Sources

• Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine — Nephron
• National Kidney Foundation. Cockcroft–Gault equation: considerations for use — derivation, the 15% for women, standardised creatinine, body weight and medication decisions
• National Kidney Foundation. CKD-EPI creatinine equation — the race-free version
• Devine BJ. Gentamicin therapy — Drug Intelligence and Clinical Pharmacy (the ideal body weight formula)
• Aminoglycosides: an update on indications, dosing and monitoring — Australian Prescriber, the adjusted body weight factor of 0.4
• A comparison of estimates of glomerular filtration in critically ill patients with augmented renal clearance — the Cockcroft–Gault and Du Bois formulas as used in practice

Limitations

• Reference only: not for choosing, starting or adjusting any medicine dose.
• For adults 18 and over with stable kidney function; not for children, dialysis, acute kidney injury or pregnancy.
• An estimate from one blood test: muscle mass, diet and some medicines change creatinine without changing kidney function.
• Accepts weight 25–350 kg, height 120–230 cm and creatinine 0.1–20 mg/dL (9–1,768 µmol/L).

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