Creatinine and creatinine clearance tests measure the level of the waste product creatinine in your blood and urine. These tests tell how well your kidneys are working. The substance creatine is formed when food is changed into energy through a process called metabolism. Creatine is broken down into another substance called creatinine, which is taken out of your blood by the kidneys and then passed out of your body in urine. See a picture of the kidneys.
Creatinine is made at a steady rate and is not affected by diet or by normal physical activities. If your kidneys are damaged and cannot work normally, the amount of creatinine in your urine goes down while its level in your blood goes up.
Three types of tests on creatinine can be done:
The blood creatinine level shows how well your kidneys are working. A high creatinine level may mean your kidneys are not working properly. The amount of creatinine in the blood depends partly on the amount of muscle tissue you have; men generally have higher creatinine levels than women.
A creatinine clearance test measures how well creatinine is removed from your blood by your kidneys. A creatinine clearance test gives better information than a blood creatinine test on how well your kidneys are working. A creatinine clearance test is done on both a blood sample and on a sample of urine collected over 24 hours (24-hour urine sample).
The levels of blood creatinine and blood urea nitrogen (BUN) can be used to find the BUN-to-creatinine ratio. A BUN-to-creatinine ratio can help your doctor check for problems, such as dehydration, that may cause abnormal BUN and creatinine levels.
Urea is a waste product made when protein is broken down in your body. Urea is made in the liver and passed out of your body in the urine. A blood urea nitrogen (BUN) test measures the amount of urea in your blood. Like creatinine, it can help your doctor see how well your kidneys are working.
A blood creatinine level or a creatinine clearance test is done to:
Do not do any strenuous exercise for 2 days (48 hours) before having creatinine tests.
Do not eat more than 8 oz (227 g) of meat, especially beef, or other protein for 24 hours before the blood creatinine test and during the creatinine clearance urine test.
Be sure to drink enough fluids during the 24-hour urine collection but do not drink coffee and tea. These are diuretics that cause your body to pass more urine.
The health professional drawing blood will:
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is no pain while collecting a 24-hour urine sample.
There is very little chance of a problem from having blood sample taken from a vein.
There is no chance for problems while collecting a 24-hour urine sample.
Creatinine and creatinine clearance tests measure creatinine levels in your blood and urine to give information about how well your kidneys are working. The creatinine clearance value is found from the amounts of creatinine in the urine and blood and from the amount of urine you pass in 24 hours. This value is the amount of blood cleared of creatinine per minute, based on your body size.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Women: 0.4-1.0 mg/dL or 36-90 mcmol/L
Men (younger than 40 years): 107-139 milliliters per minute (mL/min) or 1.8-2.3 milliliters per second (mL/sec)
Women (younger than 40 years): 87-107 mL/min or 1.5-1.8 mL/sec
Creatinine clearance values normally go down as you get older (normal values go down by 6.5 mL/min for every 10 years past the age of 20).
10:1 to 20:1
Reasons you may not be able to have the test or why the results may not be helpful include:
Other Works Consulted
- Ceriotti F, et al. (2008). Reference intervals for serum creatinine concentrations: Assessment of available data for global application. Clinical Chemistry, 54(3): 559–566.
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
|Primary Medical Reviewer||Anne C. Poinier, MD - Internal Medicine|
|Specialist Medical Reviewer||Tushar J. Vachharajani, MD, FASN, FACP - Nephrology|
|Last Revised||August 9, 2010|
Last Revised: August 9, 2010
Author: Healthwise Staff
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