eGFR Calculator

Not because creatinine enters through two terms at once -- the CKD-EPI 2021 formula's min-based and max-based creatinine terms are mutually exclusive, so only one is ever active for a given patient (whichever doesn't apply collapses to 1 and drops out). The real reason is the SIZE of whichever exponent is active: in the common case (creatinine at or above the sex-specific kappa constant), the active exponent is -1.200, while age enters through a much gentler exponential decay term (0.9938 raised to the patient's age, an effective decay rate of about -0.0062 per year) -- roughly two orders of magnitude smaller. That gap in exponent magnitude, not a count of terms, is why a given percentage change in creatinine moves the calculated eGFR more than the same percentage change in age.

They're different equations estimating related but distinct quantities. CKD-EPI eGFR is generally considered the more accurate estimate of true glomerular filtration rate and is used for CKD staging. Cockcroft-Gault creatinine clearance is an older (1976) formula that many drug product labels and dosing guidelines still specify directly for renal dose adjustment, because that's the equation the original dosing studies were validated against. The two numbers can reasonably differ for the same patient.

Kidney Function restates the same eGFR against a normal reference filtration rate of 100 mL/min/1.73m², so an eGFR of 45 reads as roughly 45% kidney function. It is capped at 100%: an eGFR above the reference does not mean more than whole kidney function, and a markedly elevated value often reflects glomerular hyperfiltration (seen in early diabetic kidney disease, pregnancy, or a high protein load) rather than extra reserve. Interpretation and Risk Level are read off the GFR category alone, against the standard 90 / 60 / 45 / 30 / 15 thresholds. None of the three is a separate measurement or a complete staging result: KDIGO stages chronic kidney disease on two axes -- the G category shown here and an albuminuria (A1/A2/A3) category from a urine albumin-to-creatinine ratio, which this calculator does not collect -- and CKD also requires the abnormality to persist for at least three months. Creatinine-based estimates are also unreliable at extremes of muscle mass or after amputation. A single reduced eGFR is a reason to repeat the test and talk to a clinician, not a diagnosis.

Earlier CKD-EPI versions (2009) included a coefficient that adjusted the result upward for patients identified as Black, based on average measured differences in creatinine generation. The 2021 revision, led by Dr. Lesley Inker and published in the New England Journal of Medicine, removed that race coefficient after concerns that using race as a proxy in a clinical algorithm could cause inaccurate, and potentially harmful, differences in care between patients. This calculator implements only the 2021 race-free version.

Partly. The CKD-EPI formula includes an age term (0.9938 raised to the patient's age) that lowers the estimate as age increases, reflecting that kidney filtration capacity gradually declines with normal aging even without kidney disease. But a patient's eGFR trend over time, and whether a given eGFR represents disease versus expected age-related decline, depends on more context than this calculator alone can provide.