eGFR Calculator

Calculator

How we calculate it

Glomerular filtration rate is how much blood your kidneys filter each minute, and it is almost never measured directly. It is estimated from serum creatinine — a waste product of muscle metabolism that healthy kidneys clear — adjusted for age and sex. This calculator uses the CKD-EPI 2021 creatinine equation, published by Inker and colleagues in the New England Journal of Medicine and recommended by the joint National Kidney Foundation and American Society of Nephrology task force. κ is 0.7 for women and 0.9 for men, and α is −0.241 and −0.302 respectively; these sex-specific constants exist because average muscle mass differs, so the same creatinine value implies different filtration. Importantly, this calculator applies no race coefficient. The earlier CKD-EPI 2009 equation included one, with the effect of reporting a higher eGFR for Black patients and potentially delaying referral; that adjustment has been withdrawn from recommended practice. Results are placed into the KDIGO G1 to G5 GFR categories, which describe a range of filtration — not a diagnosis, and not a stage of chronic kidney disease on their own.

Important limitations

• eGFR is an estimate built from creatinine, age and sex. It is not a measurement of your actual filtration rate.
• Creatinine comes from muscle, so eGFR is less reliable at the extremes of muscle mass — in bodybuilders, in people with significant muscle loss or limb amputation, and in people who are frail or malnourished.
• A high-protein meal, creatine supplements, cooked red meat shortly before the test, intense exercise and dehydration can all raise creatinine and lower the estimate without kidney function having changed.
• Some medications, including trimethoprim and cimetidine, raise serum creatinine by blocking its secretion without reducing actual filtration.
• The equation is validated in adults. Children and adolescents need a different pediatric equation.
• eGFR is unreliable in pregnancy, during acute illness, and when kidney function is changing rapidly such as in acute kidney injury.
• A trend across several results over months is far more informative than a single value, and day-to-day variation of a few mL/min/1.73m² is normal.
• One eGFR result does not establish a diagnosis. Chronic kidney disease requires evidence persisting for at least three months and is staged together with a urine albumin measurement.