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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.
The blood creatinine level shows how well your kidneys are working. A high level may mean that your kidneys aren't 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.
This 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 urea can be used to find the urea-to-creatinine ratio. This ratio can help your doctor check for problems, such as dehydration, that may cause abnormal urea and creatinine levels.
These tests are done:
You may be asked to:
If you are asked to collect urine, your doctor will give you a large container that holds about 4 L (1 gal). You will use the container to collect your urine for 24 hours.
Tell your doctor ALL the medicines and natural health products you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it..
A health professional uses a needle to take a blood sample, usually from the arm.
You collect your urine for a period of time, such as over 4 or 24 hours. Your doctor will give you a large container that holds about 4 L (1 gal). You will use the container to collect your urine.
But don't save this urine. Write down the time you began.
Each time you urinate during this time period, collect your urine in a small, clean container. Then pour the urine into the large container. Don't touch the inside of either container with your fingers.
Add this urine to the large container. Then write down the time.
The urine test will take 24 hours. The blood test will take a few minutes.
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
This test usually doesn't cause any pain or discomfort.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
There are no known risks from having this test.
These tests 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.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Blood creatinine, creatinine clearance, and urea-to-creatinine ratios can be measured.
Adaptation Date: 2/24/2022
Adapted By: Alberta Health Services
Adaptation Reviewed By: Alberta Health Services
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