Creatinine and Creatinine Clearance
Creatinine and creatinine clearance tests measure the level of the waste product creatinine (say "kree-AT-uh-neen") in your blood and urine. These tests tell how well your kidneys are working.
Another substance, creatine (say "KREE-uh-teen"), is formed when food is changed into energy through a process called metabolism. Creatine is broken down into creatinine. Your kidneys take creatinine out of your blood and pass it out of your body in urine.
If your kidneys are damaged and can't work as they should, the amount of creatinine in your urine goes down while its level in your blood goes up.
Three types of tests can be done.
Blood creatinine level
The blood creatinine level shows how well your kidneys are working. A high level may mean your kidneys are not working as they should. 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. This test gives better information than a blood creatinine test on how well your kidneys are working. The test is done on both a blood sample and on a sample of urine collected over 24 hours.
The BUN test measures the amount of urea in your blood. 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.
The levels of blood creatinine and blood urea nitrogen (BUN) can be used to find the BUN-to-creatinine ratio. This ratio can help your doctor check for problems, such as dehydration, that may cause abnormal BUN and creatinine levels.
Why It Is Done
These tests are done:
- To see if your kidneys are working normally.
- To find out if your kidney disease is changing.
- To see how well the kidneys work in people who take medicines that can cause kidney damage.
- To check for severe dehydration. Dehydration generally causes BUN levels to rise more than creatinine levels. This causes a high BUN-to-creatinine ratio. Kidney disease or blocked urine flow from your kidney causes both BUN and creatinine levels to rise.