eGFR

What is eGFR?

eGFR (estimated Glomerular Filtration Rate) is a calculated estimate of the glomerular filtration rate — the speed at which the kidneys filter blood, expressed in mL per minute per 1.73 m² body surface area. It is calculated using a formula that takes creatinine, age, and sex as inputs; the CKD-EPI equation is the current standard. Directly measuring the true GFR (via inulin clearance, for example) is a specialised test; eGFR is the practical estimate routinely derived from creatinine. eGFR inherits the limitations of creatinine: it is affected by muscle mass, hydration, creatine supplementation, and recent intensive training. People with above-average muscle mass (muscular athletes) tend to have higher serum creatinine at equivalent kidney function, so eGFR may be mildly underestimated for them. In small or elderly people with little muscle mass, eGFR can be mildly overestimated. For those groups, cystatin-C-based formulae are more accurate, though they are less routinely measured.

Why is eGFR relevant?

eGFR is the primary marker by which kidney function stages are classified internationally. The KDIGO (Kidney Disease Improving Global Outcomes) stages divide kidney function into six categories: G1 (eGFR ≥ 90, normal or high), G2 (60–89, mildly decreased), G3a (45–59, mildly to moderately decreased), G3b (30–44, moderately to severely decreased), G4 (15–29, severely decreased), and G5 (< 15, kidney failure). Each stage has different implications for monitoring, medication dosing, and risk of complications. For people with risk factors for kidney damage — diabetes, high blood pressure, chronic medication use (such as NSAIDs, lithium, or certain antihypertensives), hereditary kidney conditions, or recurrent infections — systematically tracking eGFR is critical. Kidney damage is typically silent: there are rarely symptoms until function has already declined substantially. Early detection via eGFR trends makes a material difference.

eGFR high or low — what it means

Always read eGFR together with creatinine, the trend across multiple measurements, and clinical context. A single low value right after heavy training, dehydration, or increased protein intake is almost never conclusive. For a fair reading, measure fasted, well hydrated, and at least 48 hours after strenuous effort or creatine supplementation. An eGFR above 90 mL/min/1.73 m² is generally considered normal; values between 60 and 90 can be normal in older adults or muscular individuals but warrant monitoring; a sustained fall below 60 is an indication for further kidney investigation, including urine analysis (protein-to-creatinine ratio, urine sediment), imaging, and blood pressure review. The rate of decline matters more than the absolute value: an eGFR falling by more than 5 mL/min/1.73 m² per year is a warning signal even if the absolute value is still above 60.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.