Estimated glomerular filtration rate

Various different diseases, conditions and medicines can affect the function of the kidneys. A reading of greater than 90 ml/min/1.73 m² is normal.

The estimated glomerular filtration rate (eGFR) blood test is commonly done as a routine part of monitoring people with kidney diseases or with conditions that can affect the kidneys, such as diabetes or high blood pressure. It is also often done as a routine test in many medical situations. If you are found to have chronic kidney disease (CKD) then the eGFR test is usually done at regular intervals to monitor your kidney function.

What is the estimated glomerular filtration rate?

The eGFR is a test that is used to assess how well your kidneys are working. The test estimates the volume of blood that is filtered by your kidneys over a given period of time. The test is called the estimated glomerular filtration rate because the glomeruli are the tiny filters in the kidneys. If these filters do not do their job properly then the kidney is said to have reduced or impaired kidney function.

The eGFR test involves a blood test which measures a chemical called creatinine. Creatinine is a breakdown product of muscle. Creatinine is normally cleared from the blood by the kidneys. If your kidneys are not working properly, the level of creatinine in the blood goes up. The eGFR is then calculated from your age, sex and blood creatinine level.

An adjustment to the calculation is needed for people with African-Caribbean origin. In the UK this adjustment is made by multiplying the eGFR calculation by 1.21. However, the correction needed may vary depending on how the eGFR has been calculated by your local laboratory.

eGFR calculations have not been fully validated in other ethnic groups (for example, Indo-Asians) or in subjects of mixed race. eGFR is also less reliable in Chinese patients.

Note: it is not possible to assess the eGFR accurately in people with abnormal amounts of muscle and in people who have conditions that can affect the level of creatinine. This includes:

• People with muscle wasting conditions.

• People who have had an amputation of an arm or leg.

• Malnourished people.

• Pregnancy.

• People with acute kidney injury.

• People with a lot of fluid retention (oedema).

• Children.

How to calculate the estimated glomerular filtration rate

eGFR is calculated using a formula which includes the blood level for creatinine. as well as age, gender and race. In England and Wales, the National Institute for Health and Care Excellence (NICE) recommends the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation because it is more accurate than other equations, particularly for people aged 75 years and over.