eGFR and Creatinine Clearance: CKD-EPI vs Cockcroft-Gault

eGFR (estimated glomerular filtration rate) is a calculated estimate of kidney filtering, reported in mL/min/1.73 m2, and most lab reports now use the race-free CKD-EPI 2021 creatinine equation. Cockcroft-Gault gives a different number, creatinine clearance in mL/min, which still appears in some drug labeling. Know which one a document is using before you compare numbers.

The formula

eGFR. The National Kidney Foundation describes eGFR as an estimate of how well the kidneys filter waste, usually from a blood creatinine test. Its calculator lists the CKD-EPI creatinine equation (2021) first and takes serum creatinine (mg/dL or µmol/L), age and sex. It does not take race, because the NKF/ASN Task Force recommends the race-free CKD-EPI equations. The equation page gives the result in mL/min/1.73 m2. The math includes exponents, so it is a job for a calculator, not for hand work.

Cockcroft-Gault. The classic form estimates creatinine clearance in mL/min:

CrCl = ((140 - age) x weight in kg) / (72 x serum creatinine in mg/dL), then multiply by 0.85 for a female patient.

The FDA guidance describes eCLcr in mL/min calculated with the Cockcroft-Gault equation and cites the original 1976 paper.

CKD stages. The National Kidney Foundation lists these eGFR levels:

The unit for these is mL/min/1.73 m2. The page does not print the unit, so check your lab report.

Using it in NurseTools

The eGFR & Clearance tool is in clinical review and is not available yet. The app is coming soon to the App Store, and nothing is downloadable now. The app shows a release-gates timeline: source and rights audit, clinical editorial review, independent testing, and regulatory and App Store review. There is also a “Notify me when available” switch. Nothing unlocks a tool that has not passed review. Only BMI and MAP are planned for launch.

As planned, every tool will show its sources, version and review date. The app is designed to need no account, never ask for patient data, and work offline.

Worked example

This is a made-up practice example, not a patient. Cockcroft-Gault by hand, for a made-up 70-year-old woman who weighs 72 kg with a serum creatinine of 1.2 mg/dL.

1. Age term: 140 - 70 = 70.
2. Multiply by weight: 70 x 72 = 5,040.
3. Denominator: 72 x 1.2 = 86.4.
4. Divide: 5,040 / 86.4 = 58.3.
5. Female factor: 58.3 x 0.85 = 49.6.

Result: about 50 mL/min (creatinine clearance, not eGFR). A lab report for the same made-up values would show an eGFR from the CKD-EPI equation, and the two numbers would not match exactly because they come from different equations and different units.

Limits and common pitfalls

• Do not swap the two. eGFR is standardized to 1.73 m2 of body surface area. Cockcroft-Gault is in mL/min. The FDA guidance says eGFR can be converted to mL/min by multiplying by the person’s body surface area and dividing by 1.73.
• Weight choice changes the answer. The FDA guidance says that in overweight or obese people, ideal or adjusted body weight is likely to be more accurate than actual weight. The AJHP consensus says clinicians use different weights, which makes Cockcroft-Gault results inconsistent.
• Cockcroft-Gault has known limits. The AJHP paper reports it was developed from data on 249 white males and that the female adjustment was estimated.
• Direction of travel: the FDA 2024 guidance recommends eGFR over Cockcroft-Gault for pharmacokinetic studies, and the AJHP paper notes a growing number of labels use eGFR. Some labeling still uses creatinine clearance, so follow the method named in the label and your facility policy.
• Use caution when kidney function is changing quickly. The AJHP paper says its guidance applies to stable kidney function and that a single eGFR can mislead in states such as acute kidney injury.