What is the creatinine blood test?

This test measures the level of creatinine in the blood. Creatinine is a waste product that is made when another chemical, creatine, is broken down to produce energy for the muscles. This waste product is carried by the blood to the kidneys, which filter it from the body into the urine.

Why is this test done?

This test is done to see how well your kidneys are filtering waste from your body. This test can help diagnose kidney disease and see how well treatment is working. It may also be used to diagnose some muscle diseases.

How do I prepare for the test?

• Your healthcare provider may ask you not to eat anything and to drink only water for about 8 hours before the test.
• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your provider before stopping any of your regular medicines.
• Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

This blood test is usually done with a 24-hour urine test. It is done either right before you start to collect urine or the day you finish collecting urine.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

Some of the reasons your creatinine blood level may be higher than normal are:

• Your kidneys are not working well.
• You have a kidney infection.
• You have something blocking the flow of urine, such as an enlarged prostate gland or a kidney stone.
• You have not been drinking enough fluids to replace fluid you have lost through blood loss, sweat, or urine.
• You have heart failure.
• You have decreased blood flow to the kidneys.
• You are pregnant and have high blood pressure.
• You are taking a medicine that affects your creatinine level.

Your creatinine blood level may be lower than normal if you have a muscle disease, such as myasthenia gravis or muscular dystrophy. It can also be low if you do not eat enough protein or have lost a lot of weight.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

• If you need more tests
• What kind of treatment you may need
• What lifestyle, diet, or other changes you might need to make