eGFR (CKD-EPI 2009)

eGFR by CKD-EPI 2021: race-free glomerular filtration estimation

The CKD-EPI 2021 equation (Inker et al., NEJM 2021) estimates the glomerular filtration rate from serum creatinine, and unlike the 2009 version it drops the race coefficient. You feed it creatinine (Scr, mg/dL), age, and sex. The constants are k (0.7 for women, 0.9 for men) and α (−0.241 for women, −0.302 for men): eGFR = 142 · min(Scr/k, 1)^α · max(Scr/k, 1)^(−1.200) · 0.9938^age · (1.012 if female). The result comes out in mL/min/1.73 m². The KDIGO stages run G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, and G5 <15 (the dialysis range). As an example, a man of 60 with Scr 1.0 mg/dL lands at eGFR ≈ 90, which is G2.

Clinical context

eGFR does most of the heavy lifting in CKD screening for diabetes, hypertension, and older patients, and you need it before any renal dose adjustment of drugs that are nephrotoxic or cleared by the kidney (vancomycin, gabapentin, DOACs, iodinated contrast). A value at G3b or below is what prompts a nephrology referral, and once a patient hits G5 with uremic symptoms it backs the indication for dialysis. CKD itself is defined as eGFR <60 that persists for ≥3 months, or markers of kidney damage such as albuminuria, imaging findings, or biopsy.

FAQ

Why remove race? The 2009 coefficient was empirical rather than biological. It pushed eGFR up in Black patients, which delayed both diagnosis and transplant listing. The 2021 equation performs about the same across populations without it.

When is eGFR unreliable? Anything that throws creatinine off will throw the estimate off too: extremes of muscle mass (amputees, body builders, sarcopenia), AKI, pregnancy, and creatine supplementation. When that happens, a cystatin C-based equation works as a tiebreaker.

Why 1.73 m²? That's the average body surface area for an adult, and normalizing to it lets you compare patients of different sizes. When you're dosing drugs in someone at the extremes of body size, de-index the value by multiplying by their actual BSA/1.73.

CKD-EPI or MDRD? KDIGO 2024 recommends CKD-EPI 2021. It's more accurate at GFR >60, the range where MDRD tends to come in too low.