What eGFR estimates and how it is calculated
The estimated glomerular filtration rate (eGFR) approximates how many milliliters of blood the kidneys filter per minute, normalized to a body surface area of 1.73 square meters. It is calculated from a blood creatinine level along with age and sex using equations such as the 2021 CKD-EPI formula, which no longer adjusts for race. A normal value in younger adults is often cited around 90 to 120 mL/min/1.73m2.
Because eGFR is an estimate derived from creatinine, it is most reliable as a trend over repeated measurements rather than a single number. Factors like muscle mass, hydration, and certain medications can shift creatinine and therefore the estimate.
Reading CKD stages and age-related decline
Chronic kidney disease is commonly staged by eGFR: stage 1 is 90 or above with other evidence of kidney damage, stage 2 is 60 to 89, stage 3a is 45 to 59, stage 3b is 30 to 44, stage 4 is 15 to 29, and stage 5 is below 15. Staging usually also considers albuminuria (protein in the urine), not eGFR alone.
Filtration capacity tends to decline gradually with age, so a modestly lower eGFR in an older adult is not necessarily disease. Interpretation depends on the full clinical picture. This is general educational information, not medical advice; kidney results should be reviewed with a qualified clinician.