Formal Name
Estimated Glomerular Filtration Rate
This article was last reviewed on
This article waslast modified on
15 January 2018.
At a Glance
Why Get Tested?

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 To Get Tested?

As a practical test to look for evidence of kidney damage. For a more definitive assessment of kidney function or to monitor changes in kidney function if you already have kidney disease, measurement of creatinine clearance is preferred.

Sample Required?

eGFR is an estimate of actual glomerular filtration rate, calculated using your age, weight, gender, and serum creatinine (requires a blood sample from a vein in your arm); in some formulas, race is also used in the calculation. Measured Creatinine Clearance, which gives an assessment of Glomerular Filtration Rate (GFR), is calculated from serum and urine creatinine levels and requires a blood sample from a vein in your arm and normally a 24-hour collection of urine. Calculated creatinine clearance is an estimate of creatinine clearance based on the serum creatinine value only and used when it is either not practical or possible to collect a 24 hr urine

Test Preparation Needed?

NICE guidelines advise people not to eat any meat in the 12 hours before having a blood test for eGFR creatinine.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you will be able to access your results online.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, gender, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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, then 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. 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.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm; this is sufficient for eGFR - for calculation of creatinine clearance, your weight and age are needed as well. Measured creatinine clearance requires both a blood sample taken from a vein in your arm and a 24-hour sample of urine.

Is any test preparation needed to ensure the quality of the sample?

NICE guidelines advise people not to eat any meat in the 12 hours before having a blood test for eGFR creatinine.

Accordion Title
Common Questions
  • How is it used?

    The eGFR is used to screen for and detect early kidney damage and to monitor kidney function. This is now routinely performed every time a serum creatinine concentration is requested to evaluate the status of the kidneys in those with, or at risk of, kidney damage such as individuals with diabetes or hypertension, where early intervention can prevent further damage. In the UK, NICE Guidance (CG182) states: “Whenever a request for serum creatinine measurement is made, clinical laboratories should report an estimate of GFR (eGFR)”

    Creatinine Clearance is a more accurate way to detect changes in kidney status than measurement of serum urea and creatinine, which are easier to do but cannot pick up early damage to the kidneys. eGFR or calculated creatinine clearance are based on serum creatinine, an easily performed and commonly used laboratory test. The calculation of eGFR which has been adopted in the UK uses a formula which uses the concentration of creatinine in blood, the age and sex of the patient and their ethnic origin.

  • When is it requested?

    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 damage so that measures can be taken to the stop or to at least to slow progression to more severe kidney damage. eGFR is suitable for most patients who are 18 or more years old, not pregnant or malnourished and do not have acute kidney damage. GPs and UK laboratories are now using eGFR to look for the presence of kidney damage in various 'at risk groups' including people with diabetes, blood vessel disease, heart problems, high blood pressure, obstructions to urines 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 does the test result mean?

    eGFR or Calculated Creatinine Clearance is a simple test to detect early changes in kidney function. A normal result means that kidney disease is less likely while a low value suggests that some kidney damage has occurred. Creatinine Clearance results are usually evaluated in the same way. Sometimes, in very early kidney damage (especially when the kidneys are damaged by diabetes), measured or estimated clearance may actually be high, indicating that the kidneys are working harder than normal.

    CKD stages according to eGFR and albumin to creatinine ratio (ACR) (Source) NICE guidelines (CG182)

    GFR and ACR categories and
    risk of adverse outcomes

    ACR categories,
    description & range

    A1 A2 A3
    Normal to
    mildly
    increased
    Moderately
    increased
    Severely
    increased
    <3 3-30 >30

     

     

    GFR categories,
    description
    & range

    G1 Normal &
    high
    =>90 No CKD in
    absence of markers
    of kidney damage

     Manage in primary care

    G2 Mild
    reduction
    60-89

     

     

    Manage in primary care

    G3a Mild -
    moderate
    reduction
    45-59
    G3b Moderate -
    severe
    reduction
    30-44
    G4 Severe
    reduction
    15-29
    G5 Kidney
    failure
    <15 Refer for specialist assessment
  • Is there anything else I should know?

    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 levels in their bloodstream than women or children.

    A person's GFR decreases with age and some illnesses and can increase during pregnancy.

    The calculation for eGFR is intended to be used when kidney function, and creatinine production, is stable. If a creatinine level is measured when the kidney function is changing rapidly, such as with acute renal failure, 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.

    The eGFR test may also be affected by drugs, such as gentamicin and cisplatin which can increase creatinine levels, and by any condition that decreases blood flow to the kidneys.

    The most commonly used equation for calculating the eGFR, and the one recommended by the Renal Association for general use, 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.

    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.

  • How can my GFR be determined?

    Direct measurement of the GFR is complicated and requires experienced personnel. The most commonly used method for determining the GFR is the creatinine clearance method mentioned above. However, this is liable to errors of urine collection as well as to problems with testing methods. The best method for determining the GFR is a procedure called an 'inulin clearance'.  It is not routinely used, however, because it is expensive and awkward. It involves introducing a fluid containing the marker molecule inulin (NOT insulin) into your veins (IV - intravenous infusion) and then collecting timed urines over a period of hours. The urine volumes are noted and the inulin in each sample is measured to allow determination of the GFR. Other methods of determining GFR use radioactive markers and have similar drawbacks. The UK now uses serum creatinine levels to calculate the eGFR.

  • Could I calculate my own eGFR?

    As mentioned above, eGFR is routinely calculated in the UK with all serum creatinine requests. However, if for some reason your serum creatinine only is known to you, there is an online eGFR calculator on the Renal Association website. However an eGFR calculated by a local laboratory may differ because it is likely to be more accurate than the website calculator which cannot take into account local variation in creatinine measurements.