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What is eGFR (estimated glomerular filtration rate)?
eGFR shows how well your kidneys filter the blood and is expressed in milliliters per minute, adjusted to a standard body surface area of 1.73 m². It is not measured directly but estimated from a simple blood test, serum creatinine, together with your age and sex. The calculator uses the CKD-EPI 2021 formula, currently recommended internationally, which no longer applies any correction based on race [1].
How is the result interpreted (KDIGO stages G1–G5)?
As a rough guide, under the KDIGO classification, in mL/min/1.73 m² [2]:
- above 90 — normal or high function (G1);
- 60–89 — a mild decrease (G2);
- 45–59 — a mild to moderate decrease (G3a);
- 30–44 — a moderate to severe decrease (G3b);
- 15–29 — a severe decrease (G4);
- below 15 — kidney failure (G5).
It is important to remember that a single value does not make the diagnosis. Chronic kidney disease means changes that persist for at least 3 months, and full staging also takes into account the amount of albumin lost in the urine (the test appears on the report as albuminuria or as the urine albumin-to-creatinine ratio). A low value is confirmed by repeating the test, at the interval set by the doctor who follows your diabetes, and if needed the assessment continues with a nephrologist. The final interpretation rests with your doctor.
Why does eGFR matter for people with diabetes?
Diabetes is one of the most common causes of chronic kidney disease, and kidney damage is painless and gives no warning signs for a long time. This is why guidelines recommend checking eGFR and urinary albumin regularly in people with diabetes, as a rule at least once a year. In type 1 diabetes the checks usually start a few years after diagnosis, and if the values are already abnormal they are repeated more often, at the interval set by the doctor. Early detection allows treatments that considerably slow the disease, and some medicines need their dose adjusted when kidney function declines. The eGFR is also one of the values the cardiovascular risk calculator asks for, because the kidney and the heart pull each other along.
What are the limitations of this estimate?
The formula assumes an average muscle mass. In people who are very muscular, very underweight, have had an amputation, or are pregnant, the estimate can be misleading. Creatinine also varies with hydration, a diet high in meat, or intense physical exercise in the days before the test. At normal or near-normal values it is less precise than at low values, because a small difference in creatinine changes the estimated result a great deal. The result is a guide, not a diagnosis.
Glossary terms used here