eGFR Test: Normal Range, Stages & Low Results Explained

The glomeruli are microscopic filters inside the kidneys. Glomerular filtration rate describes the volume filtered per minute. Measuring true GFR with an externally administered filtration marker is accurate but time-consuming, so routine laboratories estimate it from a blood marker, most often creatinine.^{See reference 1,See reference 4,See reference 5}

eGFR describes filtration, not every kidney job. It does not directly measure urine albumin, blood, electrolyte control, acid balance, hormone production, structure or the cause of a change. A reassuring number therefore cannot rule out every kidney problem.^{See reference 1,See reference 4}

Measured GFR, eGFR and creatinine clearance are related but not interchangeable. A 24-hour urine creatinine-clearance collection has collection and secretion errors; measured GFR uses an external marker; eGFR uses a population equation. The best method depends on the decision being made.^{See reference 1,See reference 4,See reference 6}

The usual unit, mL/min/1.73 m², means millilitres filtered per minute after indexing to a standard body-surface area of 1.73 square metres. An eGFR of 45 is therefore not proof of exactly 45% kidney function, and a move from 60 to 45 is not automatically a 25% loss of total kidney capacity.^{See reference 1,See reference 2,See reference 6}

Some laboratories report a whole number up to 90 and display higher results as “>90”. That reflects lower precision at higher GFR, not a missing test. A capped value cannot be used to calculate a precise change from 118 to 96 because neither exact number was reported.^{See reference 2,See reference 3}

A separate unit, mL/s/1.73 m², is used in some regions. NIDDK gives 0.0167 as the factor from mL/min/1.73 m² to mL/s/1.73 m². Keep the original result and unit rather than using conversion to override the laboratory's interpretation.^{See reference 2}

In the United States, the 2021 CKD-EPI creatinine equation uses standardized serum creatinine, age and sex and does not use race. The combined equation adds cystatin C. KDIGO says race should not be used in eGFR computation and advises regions to use a validated equation suited to their population.^{See reference 1,See reference 2,See reference 7}

Not every country uses the same equation. UK guidance uses its locally selected race-free approach and notes that the US 2021 equation has not been validated for the UK population. A different equation, assay calibration or rounding rule can change the reported value without proving that either result was copied incorrectly.^{See reference 1,See reference 4}

The equation name belongs with the result. Do not compare a current CKD-EPI value with an older MDRD, Cockcroft–Gault creatinine-clearance estimate or an unlabelled online calculation as if they were identical measurements.^{See reference 1,See reference 2,See reference 4,See reference 6}

Follow the ordering laboratory's instructions. eGFR itself is calculated from a blood marker; it does not require a separate kidney-filtration specimen. If urine ACR is ordered, a first-void morning midstream sample is preferred for initial albuminuria testing when practical.^{See reference 1,See reference 4}

For creatinine-based eGFR, NICE advises adults not to eat meat in the 12 hours before the blood test and advises the sample be received and processed promptly. That is a specific guideline instruction, not proof that every test requires fasting or a longer meat restriction.^{See reference 3,See reference 4}

Record hard exercise, creatine or protein supplements, acute illness, vomiting or diarrhoea and recent medicine changes. Do not stop a prescribed medicine or supplement solely because it appears on a confounder list; ask the clinician or laboratory that ordered the test.^{See reference 1,See reference 4,See reference 10}

For an adult with a first eGFR below 60 and no previous result, NICE advises repeating within two weeks to confirm it and help exclude acute deterioration. Serious illness, sharply reduced urine or dangerous symptoms can require assessment sooner; “repeat in two weeks” is not an instruction to wait during an emergency.^{See reference 3,See reference 10}

To assess a longer-term rate of progression, NICE advises at least three GFR estimates over no less than 90 days. KDIGO defines chronicity as a minimum of three months and says not to assume it from one abnormal eGFR or ACR.^{See reference 1,See reference 3}

Small changes can reflect biology and the assay. NICE notes about ±5% creatinine variability; the UK Kidney Association notes that eGFR changes up to about 10% can be non-significant; KDIGO says a change greater than 20% on a subsequent test in someone with CKD exceeds expected variability and warrants evaluation. These statements serve different clinical contexts and should not be collapsed into one universal cutoff.^{See reference 1,See reference 3,See reference 4}

An eGFR of 90 or higher is G1 and is often normal, especially in younger adults. Because equations are less precise at higher true GFR, a high reported estimate is not a measurement of “extra” kidney capacity and is not always comparable across equations.^{See reference 1,See reference 2,See reference 3,See reference 5}

Glomerular hyperfiltration is a real research and clinical concept, including in some diabetes and physiological states, but there is no single agreed universal eGFR cutoff. A systematic review found thresholds varying widely and often poorly justified. This page therefore does not label a high value as hyperfiltration.^{See reference 9}

A high eGFR does not cancel albuminuria or other kidney-damage evidence. If a report is unexpectedly high, interpret it with age, pregnancy status, body composition, glucose context, urine ACR, the equation and prior results rather than chasing a lower number.^{See reference 1,See reference 4,See reference 8,See reference 9}

For most adults and medicines, a validated creatinine eGFR is useful for dosing. But drug labels were developed with different methods, including measured creatinine clearance, Cockcroft–Gault and different eGFR equations. The relevant label and local pharmacy guidance matter.^{See reference 1,See reference 6}

CKD categories use eGFR indexed to 1.73 m². In people whose body size is far from average, a clinician or pharmacist may de-index the result for dosing by multiplying the indexed eGFR by body-surface area and dividing by 1.73. That calculation requires reliable height and weight and is not needed for self-interpreting a G category.^{See reference 1,See reference 6}

When a result is close to a dose cutoff, a medicine has a narrow therapeutic or toxic range, creatinine is unreliable, or kidney function is changing, combined creatinine–cystatin C or measured GFR may be appropriate. Do not start, stop or change a medicine dose from this article or its tool.^{See reference 1,See reference 2,See reference 6}