Creatinine and Creatinine Clearance Tests: About These Tests

What are they?

Creatinine tests measure the level of the waste product creatinine (say "kree-AT-uh-neen") in your blood and urine. These tests show how well your kidneys are working.

When the kidneys are not working well, they can't filter creatinine from the blood. So the level of creatinine in the blood goes up. The creatinine clearance (a test that measures how well your kidneys remove creatinine) goes down.

Why are these tests done?

A blood creatinine level or a creatinine clearance test is done to:

• See if your kidneys are working normally or if a medicine is affecting your kidneys.
• See if your kidney disease is staying the same or getting better or worse.

How do you prepare for these tests?

You may be asked to:

• Not do any strenuous exercise for 2 days (48 hours) before having the tests.
• Not eat more than 8 ounces of meat, especially beef, or other protein for 24 hours before the blood creatinine test and during the creatinine clearance urine test.
• Drink plenty of fluids if you are asked to collect your urine for 24 hours. But don't drink coffee or tea. These are diuretics that cause your body to pass more urine than normal.

If you are asked to collect urine, your doctor will give you a large container that holds about 1 gallon. You will use the container to collect your urine for 24 hours.

Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies 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..

How are the tests done?

A health professional uses a needle to take a blood sample, usually from the arm.

How to do the test

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 1 gallon. You will use the container to collect your urine.

• When you first get up, you empty your bladder.

  But don't save this urine. Write down the time you began.

• For the set period of time, collect all your urine.

  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.

• Don't get toilet paper, pubic hair, stool (feces), menstrual blood, or anything else in the urine sample.
• Keep the collected urine in the refrigerator for the collection time.
• Empty your bladder for the last time at or just before the end of the collection period.

  Add this urine to the large container. Then write down the time.

How long do the tests take?

The urine test will take 24 hours. The blood test will take a few minutes.

What happens after the tests?

• You will probably be able to go home right away.
• You can go back to your usual activities right away.