eGFR Reference Tool (CKD-EPI 2021 Race-Free)

What eGFR Estimates

The glomerular filtration rate (GFR) is the volume of fluid filtered from the blood through the kidney's tiny filters — the glomeruli — per minute per 1.73 m² of standardized body surface area. Because measuring true GFR requires injecting exogenous markers (such as inulin or iohexol), clinical practice relies on the estimated GFR (eGFR), calculated from serum creatinine — a waste product of muscle metabolism excreted almost entirely by the kidneys. When kidneys filter less efficiently, creatinine tends to accumulate in the blood; eGFR equations translate that into an estimate of filtration capacity.

The 2021 CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration) is the formula KDIGO 2024 guidelines typically suggest for estimating GFR in adults, and is widely used in the United States, United Kingdom, and most of Europe. It uses serum creatinine (in mg/dL), age, and biological sex. Unlike earlier equations, it applies no race-based coefficient.

Reference: Inker LA, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385:1737–1749. doi:10.1056/NEJMoa2102953

How Clinicians Categorise eGFR (KDIGO 2024 Reference)

For background context, KDIGO (Kidney Disease: Improving Global Outcomes) describes eGFR ranges that clinicians use when evaluating kidney function over time. Guidelines typically suggest that any categorisation also incorporates albuminuria categories (A1–A3) and clinical context; eGFR alone does not stage chronic kidney disease.

Why the Race Coefficient Was Removed (2021)

For over a decade, the standard 2009 CKD-EPI equation included a race-based multiplier: results for patients identified as Black were multiplied by 1.159, producing a systematically higher eGFR estimate. This adjustment was derived from observed average differences in serum creatinine between Black and non-Black participants in the development cohort — differences attributed, in part, to higher average muscle mass.

In September 2021, a joint task force convened by the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended removing the race coefficient. Their conclusion: race is a social and administrative construct, not a biological variable, and the race-based multiplier lacked a consistent physiological basis. Furthermore, the adjustment had measurable downstream consequences — Black patients with true kidney impairment could have their eGFR artificially inflated, delaying access to nephrology referral, transplant waitlisting, and other interventions. The 2021 equation eliminates this disparity, applying identical coefficients to all patients regardless of race or ethnicity.

Limits of eGFR

eGFR is an estimate, not a direct measurement of GFR. Its accuracy depends on several assumptions and is affected by factors unrelated to kidney filtration capacity:

• Muscle mass. Creatinine is a byproduct of creatine metabolism in muscle. Individuals with very high muscle mass (e.g. bodybuilders) will have higher baseline creatinine and a lower calculated eGFR even if their kidneys are healthy. Conversely, people with low muscle mass (elderly, malnourished) may have deceptively low creatinine and a falsely reassuring eGFR.
• Creatine supplementation. Oral creatine supplements are converted to creatinine and can transiently raise serum creatinine by 20–30%, lowering the eGFR estimate.
• Recent cooked meat intake. Cooking converts creatine in meat to creatinine, which is absorbed after ingestion. A large meat meal in the 8–12 hours before a blood draw can meaningfully raise serum creatinine.
• Pregnancy. GFR rises substantially during pregnancy (often by 40–50%), so the standard creatinine-based equations underestimate true GFR in pregnant individuals.
• Stability assumption. The CKD-EPI equation assumes creatinine is at steady state. In acute kidney injury, creatinine is rising rapidly — eGFR calculated in this setting dramatically overestimates true filtration rate.
• Certain medications. Trimethoprim, cimetidine, and some other drugs block tubular secretion of creatinine, raising serum creatinine without affecting GFR.

When creatinine-based eGFR may be unreliable, cystatin C-based or combined creatinine-cystatin C equations (also available in the 2021 CKD-EPI publication) provide a more accurate alternative.

When to Get Tested

eGFR is routinely reported whenever a serum creatinine is measured — most commonly as part of a basic or comprehensive metabolic panel (BMP/CMP). For healthy adults with no known kidney concerns, guidelines typically suggest checking it annually. Research suggests more frequent monitoring may be appropriate for anyone with type 2 diabetes, hypertension, cardiovascular disease, obesity, a family history of kidney concerns, or for those taking medications that may affect kidney function (e.g. NSAIDs, ACE inhibitors, SGLT2 inhibitors). People already in care for kidney concerns may follow a more frequent schedule set by their clinician.

Track Your Kidney Biomarkers with Health3

eGFR is most meaningful when tracked over time. The Health3 app lets you log every blood test result, visualize trends, and share a clean summary with your healthcare provider. Many people find it useful alongside other markers commonly tracked for kidney wellness: