eGFR Calculator

The equation was published by Inker and colleagues in the New England Journal of Medicine in 2021 and recommended by the US National Kidney Foundation and American Society of Nephrology. It estimates GFR in mL/min per 1.73 m² of body surface area: eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 if female, where Scr is creatinine in mg/dL, κ is 0.7 for women and 0.9 for men, and α is −0.241 for women and −0.302 for men. To convert µmol/L to mg/dL, divide by 88.4.

KDIGO, the international kidney guideline group, divides GFR into six categories. An eGFR of 90 or more is normal; 60 to 89 is mildly reduced, which is common with age and on its own is not kidney disease. Chronic kidney disease is diagnosed when eGFR stays below 60 for at least three months, or when there are other signs of kidney damage such as albumin in the urine, whatever the eGFR. Stages G3a and G3b (30 to 59) are the most common in people with kidney disease; G4 (15 to 29) usually means care by a kidney specialist; G5 (under 15) is kidney failure, when dialysis or a transplant may be needed.

Creatinine comes from muscle, so it depends on muscle mass as well as kidney function. Very muscular people, bodybuilders and people who eat a lot of meat just before the test can have a higher creatinine and a falsely low eGFR; people with little muscle, amputations, frailty or a plant-based diet can have a falsely high eGFR. Dehydration, a recent heavy workout and some medicines also change creatinine. Doctors therefore repeat the test, may check cystatin C as a second marker, and look at urine albumin before making a diagnosis.

The equation is for adults whose kidney function is stable. It is not reliable during sudden illness when creatinine is rising or falling quickly, in pregnancy, in children (who use different equations), for people on dialysis, or at extremes of body size. Drug doses are sometimes based on a different measure, creatinine clearance by the Cockcroft-Gault formula, so follow the advice of your pharmacist or doctor about medicines.

High blood pressure and diabetes are the two main causes of kidney disease. Keeping blood pressure and blood sugar in the target range your doctor sets, not smoking, staying active, keeping a healthy weight, limiting salt and avoiding regular use of painkillers such as ibuprofen all help protect kidney function. If your eGFR is low or falling, ask your doctor what it means for you.