Estimated Glomerular Filtration Rate (eGFR)

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

In the UK, the National Institute for Health and Care Excellence (NICE) guidance (CG182) states: “Whenever a request for serum creatinine measurement is made, clinical laboratories should report an estimate of GFR (eGFR)”

When this test is required

The eGFR can be determined, with no extra testing, at the same time that a blood sample is sent for a creatinine measurement. Since April 2006 eGFR has been routinely offered by the majority of UK laboratories. It was introduced to improve the detection of early kidney dysfunction so that measures can be taken to halt or at least, slow progression to more severe kidney damage. eGFR is suitable for most patients who are 18 or more years old, not pregnant or malnourished, do not have reduced muscle mass e.g. amputees, and do not have acute kidney injury. GPs and UK laboratories are now using eGFR to look for the presence of kidney dysfunction in various ‘at risk groups’ including people with diabetes, blood vessel disease, heart problems, high blood pressure, obstructions to urinary flow and in patients taking some commonly prescribed drugs including diuretics (water tablets) and a variety of drugs used to treat high blood pressure.

What the Test Detects

Glomerular filtration rate (GFR) is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood, while preventing loss of important proteins and blood cells. The rate refers to the amount of blood that is filtered per minute. When a person’s kidney function declines due to damage or disease, the filtration rate decreases and waste products begin to…Glomerular filtration rate (GFR) is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood, while preventing loss of important proteins and blood cells. The rate refers to the amount of blood that is filtered per minute. When a person’s kidney function declines due to damage or disease, the filtration rate decreases and waste products begin to accumulate in the blood. Chronic kidney disease (CKD) is associated with a decrease in kidney function that is often progressive. CKD can be seen with a variety of conditions, including diabetes and high blood pressure. Early detection of kidney dysfunction can help to minimise the damage. This is important, as symptoms of kidney disease may not be noticeable until as much as 30 to 40% of kidney function is lost. A measured GFR is considered the most accurate way to detect changes in kidney status, but measuring the GFR directly is complicated, requires experienced personnel, and is typically performed in a research setting. Because of this, an estimate – the eGFR – is usually used. The eGFR is a calculation based on a serum creatinine test result mainly, but serum cystatin C may substitute creatinine or be included with creatinine. Creatinine is a muscle waste product that is filtered from the blood by the kidneys and excreted into the urine at a relatively steady rate. When kidney function decreases, less creatinine is excreted and concentrations increase in the blood. Using the creatinine test result, a reasonable estimate of the actual GFR can be determined. See MoreSee Less

Preparation for the Test

NICE guidelines advise people not to eat any meat in the 12 hours before having a blood test for eGFR creatinine. Recent evidence also suggests that fish should not be eaten before having a blood test.

Sample Requirements

eGFR is an estimate of actual glomerular filtration rate and may be calculated using your age, weight, height, gender, ethnicity, serum creatinine and/or serum cystatin C (requires a blood sample from a vein in your arm)

Additional Notes

The actual amount of creatinine that a person produces and excretes is affected by their muscle mass and by the amount of protein in their diet. Men tend to have higher creatinine concentrations in their bloodstream than women or children.A person’s GFR will decrease with age and can increase during pregnancy.The calculation for eGFR is intended to be used when kidney function, and creatinine production, is stable. If serum creatinine is measured when the kidney function is changing rapidly, such as with acute kidney injury, then it will not give a useful estimate of the filtration rate. A slightly different equation should be used to calculate the eGFR for those under the age of 18. eGFR may not be as useful for those who differ from normal creatinine concentrations. This may include people who have significantly more muscle (such as a body builder) or less muscle (such as a muscle-wasting disease) than the norm, those who are extremely obese, malnourished, follow a strict vegetarian diet, ingest little protein, or who take creatine dietary supplements. Likewise, the eGFR equations are not valid for those who are 75 year of age or older because muscle mass normally decreases with age. For these individuals an eGFR based upon serum cystatin C may be more useful.The eGFR test may also be affected by drugs, such as gentamicin, cimetidine, trimethoprim and cisplatin which can increase plasma creatinine concentration , and by any condition that decreases blood flow to the kidneys.The most commonly used equation in the UK for calculating eGFR, is called the MDRD (Modification of Diet in Renal Disease study) equation. It requires a person’s serum creatinine, age, and assigned values based upon gender and race. However, the CKD-EPI equation based upon serum creatinine, age, gender and ethnicity is recommended by NICE CG182.When an improved assessment of eGFR is needed a serum cystatin C test can be used. This test is not currently available in all UK laboratories.

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