eGFR - estimated Creatinine Clearance

You will need a blood sample taken from a vein in your arm. NICE guidelines advise you not to eat any meat or fish in the 12 hours before your blood test. Protein from meat or fish can temporarily raise creatinine levels, which affects the eGFR calculation. 

You do not need to fast from other foods or drinks unless your doctor advises otherwise. Tell your doctor about any supplements you take, particularly creatine supplements, as these can also affect the result.

What the test measures 

Your kidneys contain millions of tiny filters called glomeruli. These filter waste products and excess fluid from your blood, while keeping important substances like proteins and blood cells in your body. 

The glomerular filtration rate (GFR) measures how much blood your kidneys filter every minute. A healthy kidney has a high filtration rate. When the kidneys are damaged or diseased, this rate falls and waste products begin to build up in the blood. 

Because measuring the true GFR directly is complex and not practical for routine care, a calculated estimate — the eGFR — is used instead. Your eGFR is worked out from your blood creatinine level, along with your age and sex. Creatinine is a waste product made by your muscles at a steady rate and filtered out by healthy kidneys. 

What your results mean 

eGFR is reported in millilitres per minute per 1.73 m² (mL/min/1.73m²). This standard unit allows results to be compared between people of different body sizes. A higher number means your kidneys are filtering more blood and working better. 

NICE uses eGFR alongside the urine albumin-to-creatinine ratio (ACR) to categorise kidney function and guide care. These two results together give a fuller picture of kidney health than eGFR alone. 

eGFR 90 or above (G1 — normal or high) 

An eGFR of 90 or above is generally considered normal. If there are no other signs of kidney damage — such as protein in the urine — this result alone does not indicate kidney disease. 

However, a high eGFR can sometimes be seen in the early stages of diabetic kidney disease, when the kidneys are working harder than normal. Your doctor will consider your full picture. 

eGFR 60 to 89 (G2 — mildly reduced) 

A mild reduction in eGFR may still be within the normal range for your age. Kidney function naturally declines a little as we get older. Your doctor will look at whether there are any other signs of kidney damage, such as raised protein in your urine, before deciding whether further investigation is needed. 

eGFR 45 to 59 (G3a — mild to moderate reduction) 

This range indicates a mild to moderate reduction in kidney function and falls within stage 3a of chronic kidney disease (CKD). Most people at this stage are managed in primary care by their GP. Your doctor will monitor your eGFR regularly and look for and treat any underlying causes. 

eGFR 30 to 44 (G3b — moderate to severe reduction) 

This indicates a more significant reduction in kidney function (CKD stage 3b). Your GP will monitor you closely. Depending on the trend in your results and your other health factors, a referral to a kidney specialist (nephrologist) may be considered. 

eGFR 15 to 29 (G4 — severe reduction) 

At this level, kidney function is severely reduced (CKD stage 4). You are likely to be referred to a kidney specialist. Planning for kidney replacement therapy — such as dialysis or a kidney transplant — may begin at this stage. 

eGFR below 15 (G5 — kidney failure) 

An eGFR below 15 indicates kidney failure (CKD stage 5). You will usually be under the care of a specialist kidney team, and treatment to replace or support kidney function is typically needed. 

If your eGFR is in a normal range and stable, your doctor may simply repeat the test at your next routine appointment. No immediate action is usually needed. 

If your eGFR is mildly reduced, your doctor will usually repeat it after a few weeks to see whether it stays the same or changes. A single low result does not always mean kidney disease — short-term causes such as dehydration or a recent illness can temporarily lower your eGFR. 

If your eGFR is consistently low or falling over time, your doctor will investigate the cause, treat any underlying conditions, and monitor you more closely. Depending on your eGFR level, you may be referred to a kidney specialist. People with an eGFR below 15 will usually be under specialist kidney care. 

• Muscle mass: people with more muscle naturally produce more creatinine, which can give a lower (worse) eGFR reading than their actual kidney function. 
• Low muscle mass: people with muscle-wasting conditions, older adults, or those who are malnourished may have a falsely high (better) eGFR. 
• Diet: eating meat or fish in the 12 hours before your test can temporarily raise creatinine and lower your eGFR. A strict vegetarian diet may have the opposite effect. 
• Creatine supplements: these raise creatinine levels and can lower your eGFR result. Always tell your doctor if you take them. 
• Medicines: some drugs — including certain antibiotics (such as gentamicin and trimethoprim), some blood pressure medicines, and chemotherapy drugs (such as cisplatin) — can affect creatinine levels or kidney function. 
• Pregnancy: eGFR naturally rises during pregnancy because the kidneys filter more blood. Standard eGFR values should not be used to assess kidney function in pregnant women. 
• Age: eGFR naturally falls with age as kidney function gradually declines. This does not always mean kidney disease. Cystatin C‑based eGFR may be more accurate in people aged 75 and over. 
• Acute illness: eGFR assumes stable kidney function. During an acute kidney injury, when kidney function is changing rapidly, the eGFR figure is unreliable. 

The eGFR works best when considered alongside the urine albumin-to-creatinine ratio (ACR). Albumin is a protein that healthy kidneys keep out of the urine. A raised ACR suggests early kidney damage, even when eGFR is normal. 

Your doctor may also check your urine protein-to-creatinine ratio (UPCR), blood urea, electrolytes (sodium and potassium), and calcium. These give a fuller picture of how your kidneys are working and whether any complications are developing. 

If a more accurate measurement of kidney function is needed — for example, before certain treatments — a cystatin C test may be requested. This marker is less affected by muscle mass and may give a better estimate of true kidney function in some groups.

CKD means the kidneys have been damaged and do not filter blood as well as they should. It is often caused by diabetes or high blood pressure. It can progress slowly and may have no symptoms for years. Early detection and treatment can significantly slow its progression.