eGFR - Calc. Creatinine Clearance
At a Glance
Why Get Tested?
To determine the function of your kidneys
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?
Creatinine Clearance can be 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.
The Test Sample
What is being tested?
Creatinine Clearance gives an assessment of glomerular filtration rate (GFR) which in turn 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. 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.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm; your weight and age are needed for calculation of creatinine clearance as well. Measured creatinine clearance requires both a blood sample taken from a vein in your arm and a 24-hour sample of urine.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
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. If kidney damage is detected early, it may be possible to prevent further damage, with treatment of high blood pressure, diabetes, or other diseases that can damage the kidney. eGFR or calculated creatinine clearance is 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?
Since April 2006 eGFR 'estimated GFR' or calculated Creatinine Clearance has been routinely offered by the majority of UK laboratories. It has been 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.
Is there anything else I should know?
Creatinine Clearance can increase during pregnancy.
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
