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Creatinine and Creatinine Clearance Tests: About These Tests

How the kidneys work

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. Blood creatinine level can also be used to calculate the estimated Glomerular Filtration Rate (eGFR).

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:

  • Drink plenty of fluids if you are asked to collect your urine for 24 hours.

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 affect the results of the test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.

How to do the test

For the urine tests

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.

  • 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.

For the blood test
A health professional takes a sample of your blood.

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.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

Go to https://www.healthwise.net/patientEd

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