Optimize
← All biomarkers
Kidneys

eGFR

eGFR is a calculated estimate of how fast your kidneys filter your blood, giving a general picture of kidney function.

What is eGFR?

eGFR is a calculated estimate of how quickly the kidneys filter blood. It is derived from creatinine, age, and sex. It is a practical estimate — not a direct measurement of kidney function. eGFR inherits the limitations of creatinine. In people with a lot of muscle mass, eGFR can be slightly underestimated. In older people with little muscle mass, it can be slightly overestimated. Creatine supplementation, dehydration, and intense training all affect the value. Always read eGFR together with creatinine and in the context of body composition and hydration.

Why is eGFR relevant?

eGFR is the standard measure used to classify kidney function internationally. The higher the value, the better the kidneys filter. A falling eGFR across multiple measurements is the earliest and most reliable signal that kidney function is declining. Kidney damage is almost always silent: symptoms rarely appear until function has already declined substantially. For people with risk factors — high blood pressure, diabetes, certain long-term medications, or hereditary kidney conditions — systematically tracking eGFR trends is critical. Early detection makes a meaningful difference.

eGFR high or low — what it means

Always read eGFR alongside creatinine and the trend across repeat measurements. A single low value right after hard training, dehydration, or increased protein intake is rarely conclusive. Test fasted, well hydrated, and at least 48 hours after strenuous effort or creatine supplementation. A persistently declining eGFR warrants closer kidney investigation, even if the absolute value still looks reasonable. The rate of decline matters more than any single reading. A markedly and persistently reduced eGFR calls for urine analysis, blood pressure review, and medical guidance.

eGFR reference ranges

Normal (G1)Normal kidney function≥ 90 ml/min/1.73m²
Mildly reduced (G2)Abnormal only with additional signs of kidney damage60–89 ml/min/1.73m²
Mild-moderate (G3a)45–59 ml/min/1.73m²
Moderate-severe (G3b)30–44 ml/min/1.73m²
Severely reduced (G4)15–29 ml/min/1.73m²
Kidney failure (G5)< 15 ml/min/1.73m²

Stages per KDIGO/NHG. An eGFR < 60 ml/min/1.73m² counts as abnormal at any age, but it naturally declines by ~0.5–1.0 per year from around age 30. A single value is an estimate; the trend and context (muscle mass, hydration) matter more.

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

Read about our scientific approach →

Frequently asked questions

What is a normal eGFR value?

An eGFR of 90 ml/min/1.73m² or higher is considered normal (stage G1). Between 60 and 89 (G2) kidney function is mildly reduced, which on its own is often not a concern — only below 60 ml/min/1.73m² is the result considered abnormal. The value also declines naturally by about 0.5 to 1 point per year from roughly age 30, so a somewhat lower eGFR later in life is partly expected.

What does a low or falling eGFR mean?

The lower the eGFR, the less blood your kidneys filter per minute. Stages run from G3a (45–59) and G3b (30–44) through G4 (15–29) to G5 — kidney failure — below 15 ml/min/1.73m². More important than any single number is the trend: an eGFR that keeps falling across repeat measurements is the earliest and most reliable signal that kidney function is declining, even when the absolute value still looks reasonable.

When is a low eGFR a concern?

A persistently confirmed eGFR below 60 ml/min/1.73m² warrants closer kidney investigation, especially with risk factors such as high blood pressure, diabetes, or long-term medication. Below 30 (G4) and certainly below 15 (G5) indicates a serious loss of kidney function requiring medical guidance. A single low result right after hard training, dehydration, or a high-protein meal is rarely conclusive — repeat the test fasted and well hydrated.

Is a high eGFR bad?

No — with eGFR, the higher the value, the better your kidneys filter. A value of 90 ml/min/1.73m² or higher is normal and not a concern in itself. The attention goes to low or falling values instead. That said, eGFR is a calculated estimate, so a notably high or strongly fluctuating result should always be read together with creatinine.

Why does my eGFR vary between tests?

eGFR is a calculated estimate from creatinine, age, and sex — not a direct measurement. Muscle mass, hydration, recent intense training, and creatine supplementation all affect the result, and the lab method adds variation too. That is why clinicians only treat a difference of about 15% between two readings as meaningful, and why eGFR is always interpreted together with creatinine and the trend over time.

Related biomarkers

Creatinine
Creatinine is a waste product of your muscles that your kidneys filter from the blood — a measure of kidney function.

eGFR is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

See the full test