The 2021 CKD-EPI creatinine equation is the current standard for estimating glomerular filtration rate in adults, and its headline change is the removal of the race coefficient. The 2009 equation had adjusted upward for Black patients on the assumption of higher average muscle mass; the 2021 equation drops that adjustment because the race-based correction was found to overestimate GFR in Black patients and delay recognition of kidney disease. The result is a single equation applied to everyone.
The method
The equation takes serum creatinine, age, and sex. It is a two-slope exponential: below a creatinine-to-κ ratio of 1 the slope is gentler, and above it the slope steepens, which is what gives the equation its better accuracy in the near-normal GFR range compared with MDRD-4. The output is reported in mL/min/1.73 m², indexed to body surface area. KDIGO stages CKD from the GFR and the albuminuria category together, so the eGFR alone is only half of the staging picture.
A worked example
A 62-year-old woman with a serum creatinine of 1.4 mg/dL. The equation returns an eGFR of roughly 40 mL/min/1.73 m², which is CKD stage 3b. If her urine albumin-to-creatinine ratio is 300 mg/g or more, she is in KDIGO category G3bA3 — the highest risk grid — and warrants nephrology referral. The same creatinine in a 30-year-old man would return a higher eGFR because age and sex both enter the equation, which is why the raw creatinine value alone is never interpreted without them.
Common mistakes
The equation is for adults with stable kidney function; it is not validated in children, in pregnancy, or during acute kidney injury, where creatinine is changing faster than the equation assumes. It estimates creatinine-based GFR only — it does not capture tubular function, and it can mislead in people with unusually high or low muscle mass, such as bodybuilders, amputees, or the frail elderly. Cystatin C-based equations are more accurate in those groups. Finally, the 2021 equation gives slightly lower eGFR values than the 2009 equation in Black patients, which is the intended correction, not an error.
Source and disclaimer
Source: Inker LA et al., "New creatinine- and cystatin C-based equations to estimate GFR without race", New England Journal of Medicine, 2021; and the KDIGO 2024 clinical practice guideline for the evaluation and management of CKD. Educational use only — eGFR must be interpreted with the clinical context and is not a substitute for a nephrology assessment.