eGFR explained: your estimated kidney filtration

What eGFR measures

Each kidney contains around a million tiny filters called glomeruli. The glomerular filtration rate (GFR) is the total amount of blood these filters clean each minute. It is the best overall measure of how well the kidneys are working.

Measuring GFR directly needs special tests with injected markers and timed samples, which are rarely done outside research and specialist centres. Instead, labs estimate it. That estimate is the eGFR.

eGFR is reported in mL/min/1.73m²: millilitres of blood filtered per minute, adjusted to an average adult body surface area of 1.73 square metres so that results can be compared between people of different sizes.

How eGFR is calculated

eGFR is not a separate blood test. It comes from the same blood sample as your creatinine test. The lab puts your creatinine result, age and sex into an equation developed from large studies in which GFR was measured directly.

The equation recommended in most current guidance is CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration). The 2021 version no longer includes a race adjustment. Some labs still use an older version of CKD-EPI or an older equation called MDRD, and a few report a creatinine clearance calculated with the Cockcroft-Gault formula, which is mainly used for medicine dosing. If you compare eGFR results from different labs, the equation used may explain small differences. You can ask the lab which one it uses.

KDIGO 2024 guidance recommends estimating GFR with a validated equation rather than relying on creatinine alone. Where a more accurate estimate matters, it suggests adding a second marker called cystatin C, which is less affected by muscle mass. The combined result is written as eGFRcr-cys.

If your report shows creatinine but no eGFR, your clinician can calculate it. This site does not offer an eGFR calculator, because the number needs to be read by someone who knows your history.

Why it is ordered

eGFR is used to check kidney function in people with diabetes, high blood pressure, heart disease or a family history of kidney disease, to decide medicine doses, to prepare for scans with contrast dye and to follow chronic kidney disease (CKD) over time. It is usually reported automatically whenever creatinine is tested.

Sample and preparation

The sample is an ordinary blood draw from the arm. Because eGFR is calculated from creatinine, the same preparation applies: if advised, avoid a large meal of cooked meat in the 12 hours before and avoid heavy exercise just before the test. Drink normally. Tell your clinician about any supplements and medicines.

How results are reported: the G categories

KDIGO groups eGFR into categories called G1 to G5. These categories describe the level of filtration. They are used together with urine albumin to describe chronic kidney disease, and they are only one part of the picture.

Three points make this table easier to read correctly:

• G1 and G2 are not CKD by themselves. An eGFR of 60 or above counts as CKD only if there is another sign of kidney damage, such as albumin in the urine or a structural change seen on a scan, present for more than 3 months.
• One result does not set a category. CKD requires the change to last more than 3 months, so a single low eGFR is usually repeated.
• Many labs print ">90" or ">60" rather than an exact number at the top of the range, because the equation is less precise there.

eGFR naturally falls slowly with age. A value in G2 or G3a in an older person can have a different meaning from the same value in a young adult. That is a judgement for your clinician. Our page on CKD stages explains how G and A categories are combined.

What can affect the result

Anything that changes creatinine without changing filtration also changes eGFR. This includes:

• very high or very low muscle mass, including amputation, long illness or bodybuilding
• a recent large meal of cooked meat, heavy exercise or creatine supplements
• dehydration from heat, vomiting or diarrhoea
• some medicines that change how creatinine is handled by the kidney

The equations also have known limits. They are less reliable:

• when kidney function is changing quickly, for example in a sudden illness (acute kidney injury), because creatinine takes time to catch up
• in pregnancy
• in children, for whom different equations are used
• at extremes of body size or in people with very unusual diets

What eGFR cannot tell you on its own

eGFR is an estimate of filtration. It does not show whether the kidney filters are leaking protein, and it does not explain the cause of any change. KDIGO 2024 places urine albumin, measured as the urine albumin to creatinine ratio (ACR), alongside eGFR in every CKD assessment. Someone can have a normal eGFR and still have kidney damage shown by albumin in the urine.

The pattern over time matters more than any single value. A steady eGFR of 55 over several years tells a different story from an eGFR that has dropped from 80 to 55 in a year. Keep copies of your reports from each lab visit, whether in Nyali, Bamburi or on Mombasa Island, so the trend can be seen.

Related tests

• Creatinine test: the blood result eGFR is calculated from.
• Urine ACR: the partner test for albumin in urine.
• Kidney function tests: urea, electrolytes and creatinine together.
• Kidney ultrasound: shows the size and structure of the kidneys.

When to discuss your result with a clinician

Arrange a review if your eGFR is below 60, if it has fallen compared with an earlier result, or if you have diabetes or high blood pressure and have never had a urine ACR test. An eGFR below 30, or a fast fall, usually calls for prompt review, and your clinician may discuss a referral to a kidney specialist (nephrologist). Our guide on when to see a nephrologist explains how that decision is usually made.

Common questions

Is eGFR a percentage of kidney function?

Not exactly. eGFR is reported in mL/min/1.73m², not as a percentage. The number is sometimes described loosely as a percentage because a healthy young adult's value is around 100, but this is only a rough way of speaking and can mislead.

Can my eGFR go up again?

eGFR changes from test to test. It can improve after dehydration or a short illness settles, or after a medicine is reviewed. In long-standing kidney disease the aim of care is often to slow any decline. Your clinician will look at the trend across several results.

My eGFR is 65. Do I have kidney disease?

An eGFR of 60 or above does not on its own mean chronic kidney disease. CKD in this range is only considered when there is another sign of kidney damage, such as albumin in the urine, present for more than 3 months. Discuss the full picture, including urine ACR, with your clinician.

This page explains what a test or condition involves. It is not a diagnosis and does not replace advice from a doctor who knows your history. Your results should be interpreted together with your symptoms, other tests and a clinical assessment. Medical disclaimer.