Also known as:
Name: Creatinine clearance
Related tests: Creatinine, eGFR, GFR
Why is the test done?
To help diagnose and assess kidney dysfunction.
When is it done?
If your doctor thinks you have problems with the way your kidneys are working (for example, a blockage in the kidneys or acute or chronic kidney failure) or another condition such as congestive heart failure.
What samples are required?
Both a urine sample (24-hour urine collection) and a blood sample taken from a vein in the arm.
What is being analysed?
The test measures the amount of creatinine in the blood and urine to assess the kidneys’ filtering capacity.
Creatinine is a waste product derived from creatine, a nitrogen-based organic compound used by the muscles to store and transfer energy. The amount of creatinine produced in the body depends on muscle mass and is constant in each person. Creatinine is removed from the body by filtering units called glomeruli as blood passes through the kidneys. The amount of creatinine removed from the blood depends on the filtering capacity of the glomeruli and the rate at which blood is delivered to the kidneys. If the glomeruli are damaged or diseased, or if blood flow is slowed, less creatinine will be removed from the blood and passed into the urine.
Creatinine clearance is a calculation that gives a general assessment of the amount of blood filtered over 24 hours. There are several versions of this calculation. Each involves measuring the creatinine concentration in a blood sample taken around the time of the 24-hour urine collection, and measuring the amount of urine passed in those 24 hours. Since the amount of creatinine produced depends on muscle mass, some calculations also include a correction factor that takes into account the patient’s body surface area (based on their weight and height).
How is the sample collected for testing?
The test requires a 24-hour urine collection and a blood sample taken at the start or end of the urine collection. The blood sample is taken from a vein in the arm.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Creatinine clearance is used to assess the rate and efficiency of kidney filtration. The test helps detect kidney dysfunction and/or reduced blood flow to the kidneys. In patients with chronic kidney disease or congestive heart failure (which slows blood circulation), creatinine clearance may be requested to monitor the progression and severity of the disease.
When is it requested?
Creatinine clearance may be requested whenever the doctor wants to assess how efficiently the kidneys are filtering. It may be requested when blood creatinine rises, with a known or suspected kidney disorder, or when blood flow to the kidneys is reduced because of congestive heart failure.
What does the test result mean?
Any disease or condition that affects the glomeruli can reduce the kidneys’ ability to clear creatinine and other waste products from the blood. In these cases blood creatinine will rise and creatinine clearance will fall, because the kidneys are less able to remove it from the blood. Creatinine clearance also falls when blood supply to the kidneys is reduced because of congestive heart failure, a blockage within the kidneys, or acute or chronic kidney failure. Creatinine clearance may occasionally rise during pregnancy, with exercise and with diets rich in meat.
Patients with one kidney that works well and one that does not usually have normal creatinine clearance, because the working kidney makes up for the diseased one.
Is there anything else I should know?
Creatinine clearance tends to fall with age, as does the glomerular filtration rate (the rate at which the glomeruli filter the blood). Some medicines, such as aminoglycosides, cimetidine, cisplatin and cephalosporins, can reduce creatinine clearance. Diuretics have the opposite effect.
1. What should I do if I forget to keep part of the 24-hour urine?
2. How accurate is this test?
3. Can I do the test at home?
1. What should I do if I forget to keep part of the 24-hour urine?
If you do not collect all the urine over 24 hours, the test is not valid. You will need to get another container from your doctor or the laboratory and start the collection again on another day.
2. How accurate is this test?
There are even more accurate tests than this one. They require tracers to be infused into the patient and are more expensive. For most clinical purposes, the accuracy of creatinine clearance is sufficient.
3. Can I do the test at home?
No. This test requires analyses and calculations that only experienced healthcare staff can carry out.