A worked example: male, creatinine 1.0 mg/dL, age 50
A 50-year-old male with a serum creatinine of 1.0 mg/dL has an estimated GFR of 91.7 mL/min/1.73m² — comfortably in stage G1, the normal range (≥90).
Why the formula needs age and sex, not creatinine alone
Creatinine is a waste product from muscle metabolism, so its normal baseline level already varies by typical muscle mass — the 2021 CKD-EPI equation adjusts for that using age (filtration naturally declines over a lifetime) and sex (differing typical muscle mass), rather than treating every creatinine reading the same regardless of who it came from.
A second example showing reduced function: female, creatinine 1.2, age 65
A 65-year-old female with a serum creatinine of 1.2 mg/dL has an estimated GFR of 50.2 mL/min/1.73m² — stage G3a, a mildly-to-moderately decreased range, despite a creatinine level that might look only slightly elevated on its own.
The five stages: G1 through G5
G1 (≥90, normal), G2 (60-89, mildly decreased), G3a (45-59), G3b (30-44), G4 (15-29), and G5 (<15, kidney failure) — a formal CKD diagnosis also requires evidence of kidney damage alongside a persistently low eGFR, not a single reading in isolation.
Why the 2021 equation dropped its earlier race adjustment
Earlier versions (2009 CKD-EPI, MDRD) included a race coefficient that the 2021 update removed, following evidence that race isn't a reliable biological proxy for kidney function and its use could delay care for Black patients — the current formula uses only creatinine, age, and sex.