Blood (Serum) Creatinine Test

What is the blood creatinine test?

This test measures the amount of creatinine in the blood. Muscles make creatinine when another chemical, creatine, is broken down to produce energy for the muscles. Creatinine is carried by the blood to the kidneys, which filter it from the body in the urine. (Creatinine can be measured in urine as well as blood.)

Why is this test done?

Creatinine is measured to see how well your kidneys are working. It can help diagnose kidney disease. This test is a more sensitive test of kidney function than another test called the BUN test.

This test may be used with another test called the BUN test to see if you are dehydrated.

How do I prepare for the test?

• Your health care provider may ask you not to eat anything and to drink just 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 health care provider knows about any medicines, herbs, or supplements that you are taking.
• Talk to your health care provider if you have any questions.

How is the test done?

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes and sent to a lab.

Having this test will take just a few minutes of your time. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.

How will I get the test result?

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

What does the test result mean?

The normal range for creatinine in the blood is 0.8 to 1.4 milligrams per deciliter (mg/dL). The normal range may vary slightly from lab to lab. Normal ranges are usually shown next to your results in the lab report.

Your creatinine level may be higher than normal because:

• Your kidneys aren't working well.
• You have a kidney infection.
• You have something blocking the flow of urine in your system (such as an enlarged prostate gland or a kidney stone).
• You are dehydrated.
• You have congestive heart failure.
• You have decreased blood flow to the kidneys.
• You are pregnant and have high blood pressure (preeclampsia, or toxemia of pregnancy).

Some medicines can cause the creatinine level to be higher than normal, such as:

• certain blood pressure medicines including ACE inhibitors (such as captopril and enalapril)
• nonsteroidal anti-inflammatory drugs (such as ibuprofen or naproxen)
• diuretics, such as furosemide
• some antibiotics including aminoglycosides (for example, gentamicin) and cephalosporins (for example, cefoxitin and cimetidine).

Your creatinine level may be lower than normal because:

• You have a muscle disease such as myasthenia gravis or muscular dystrophy.

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 and current health. Sometimes a test needs to be repeated to check the first result. Talk to your heath care provider about your result and ask questions.

If your test result is not normal, ask your health care provider:

• if you need additional tests
• what you can do to work toward a normal value
• when you need to be tested again.