Estimated Glomerular Filtration Rate (eGFR)

What is Estimated Glomerular Filtration Rate (eGFR)?

eGFR is a calculated estimate of how many milliliters of blood your kidneys filter each minute, based on a blood creatinine result plus your age and sex.

Your kidneys filter your blood continuously, and the rate at which they do it, glomerular filtration rate, is the standard measure of how well they're working. Measuring GFR directly means infusing a marker substance like inulin and timing its clearance, which is accurate but impractical outside research. So labs estimate it instead: creatinine, a waste product from muscle breakdown, builds up in your blood when filtration slows down. Plug your creatinine result into an equation along with your age and sex, and you get eGFR, expressed in milliliters per minute per 1.73 square meters of body surface area. The equation itself has changed. The CKD-EPI formula introduced in 2009 included a coefficient that assigned Black patients a higher eGFR than a white patient with the same creatinine, age, and sex, on the assumption that average muscle mass differed by race. Critics argued the adjustment used race as a biological proxy and could delay Black patients' referral for transplant evaluation or specialty care. In 2021, the CKD-EPI collaboration published a new equation, developed and validated across more than 12,000 people, that removed race entirely. According to the National Institute of Diabetes and Digestive and Kidney Diseases, this race-free formula estimates GFR about 4% higher than measured GFR in non-Black patients and about 4% lower in Black patients on average, a tradeoff that shifted the equation's bias rather than eliminating it. A second version of the 2021 equation adds cystatin C, a protein filtered by the kidneys that isn't affected by muscle mass, alongside creatinine. NIDDK and the National Kidney Foundation both describe this combined creatinine-cystatin C equation as more accurate than creatinine alone, particularly useful for confirming a diagnosis in people whose creatinine may not reflect true kidney function.

Typical reference context

The chronic kidney disease staging system below comes from KDIGO's 2024 clinical practice guideline and matches the current National Kidney Foundation staging chart. These are published clinical categories, not an interpretation of any individual result, and a single eGFR reading in the G3-G5 range needs to persist for three months or more, alongside other evidence of kidney damage in the earlier stages, before it counts as chronic kidney disease.

What changed recently

Adoption of the race-free equation is still incomplete. A June 2026 Healio report on a National Kidney Foundation and pharmacy-organization coalition cites the most recent national survey putting roughly two-thirds of US laboratories on the race-free 2021 equation, with holdouts concentrated among smaller independent labs and point-of-care analyzers still hardwired for the old formula. The coalition's stated goal is 100% adoption, and the FDA has separately recommended the race-free equation for dosing decisions on newer medications.

Meanwhile, validation work continues outside the US population the equation was built from. A January 2025 study in the American Journal of Nephrology tested the race-free equations against older versions in 1,727 Korean patients with chronic kidney disease and found comparable accuracy for predicting complications like anemia and high potassium, with median differences between old and new equations of 1.6 to 2.5 mL/min/1.73m². It's one data point, not a global consensus, but it supports the equation holding up reasonably well beyond the US cohorts it was originally developed on.

Tests often checked alongside this

• Creatinine — the blood measurement eGFR is calculated from; see it as the raw number behind the estimate.
• Cystatin C — an alternate filtration marker some labs add to creatinine for a more accurate combined eGFR, especially when muscle mass might skew a creatinine-only result.
• Urine albumin-to-creatinine ratio (ACR) — paired with eGFR for full CKD staging, since KDIGO's system classifies kidney disease by GFR category and albuminuria category together, not GFR alone.

What can affect eGFR's accuracy

The equation was built and validated on large adult populations, so it gets less reliable at the edges. The National Kidney Foundation lists pregnancy, age over 70, unusually high or low muscle mass, cirrhosis, nephrotic syndrome, a past solid organ transplant, and certain medications as situations where a creatinine-based eGFR can be less precise. It also tends to lose sensitivity at the high end, meaning it can miss early declines in kidney function before creatinine has risen much. None of this is something to self-diagnose around; it's context for the number your doctor is already looking at.

What to ask your doctor

• Was my eGFR calculated with creatinine alone, or with the combined creatinine-cystatin C equation?
• Do any of the factors that affect eGFR's accuracy, like muscle mass or a past organ transplant, apply to me?
• If my eGFR is outside the normal range, does it need a repeat test to confirm before it's called chronic kidney disease?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Terms of Use.

Frequently asked questions