What is the C-reactive protein (CRP) test?

This test is a blood test used to check the level of a substance made by the liver called C-reactive protein, or CRP. The level of CRP in your blood goes up when there is inflammation in the body. There are 2 different CRP tests.
standard CRP
high-sensitivity CRP (hs-CRP, also called ultra-sensitive CRP or us-CRP).
Why is this test done?

The CRP test may help your healthcare provider diagnose and treat a medical problem you are having. A high CRP suggests that you have a disease that is causing inflammation, such as an infection, inflammatory bowel disease, or some types of arthritis or other autoimmune diseases. It cannot show exactly what is causing your illness but it can be an important test for narrowing down the list of possible causes. It can help your provider know what other tests you might need. It also is a way to see how well your treatment for a disease is working. If your treatment is reducing inflammation, your CRP will get lower.

The high-sensitivity CRP test can measure much smaller amounts of CRP than the standard CRP test. It is used to check for inflammation of the circulatory system (blood vessels). When the result of this test is high, some studies have suggested that it is a risk factor for coronary artery (heart) disease.

The hs-CRP test is recommended only if you have a moderate risk of heart disease. It is done to see if you should have more treatment to help prevent a heart attack or other problems caused by heart disease. This test is not currently recommended as routine screening if you have a low or high risk of heart disease. If you have a high risk based on other factors, you should be treated for heart disease no matter what your CRP is. Your healthcare provider will evaluate your risk for heart disease and determine if you should have this test.
How do I prepare for this test?

Usually no preparation is needed for this test.
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 for testing.

Having this test will take just a few minutes of your time.
How will I get the test results?

Ask your healthcare provider when and how you will get the results of your test.
What do the test results mean?

The normal range for the CRP varies with age, gender, and the method used to do the test. Normal ranges may vary from lab to lab. They are usually shown in parentheses next to your test results on the lab report. Talk to your healthcare provider for an interpretation of your test results. Be sure your provider knows about all of the medical problems you are having and all of the medicines you are taking, including nonprescription medicines and supplements, because they may affect the test results.

According to the American Heart Association, the results for the high-sensitivity CRP can be interpreted as follows:
Your risk of heart disease is low if your hs-CRP level is lower than 1.0 milligrams per liter (mg/L).
You have an average risk of heart disease if your levels are between 1.0 and 3.0 mg/L.
You have a high risk for heart disease if your hs-CRP level is higher than 3.0 mg/L.

If your hs-CRP is high, your provider will discuss changes you can make to have a healthier lifestyle. Your provider may also recommend daily aspirin or statin medicine (medicine that is used to lower cholesterol).

It is important to remember that the CRP or hs-CRP may be high because of inflammation in other parts of your body, such as infection, arthritis, or other diseases.
What if my test result isn’t normal?

Many things can cause a high CRP. Your healthcare provider will use the result of your CRP test, the history of your illness, your physical exam, and any other tests you may have had to arrive at a diagnosis.

The CRP may be tested again over weeks or months to follow the course of your illness or to see how well your treatment is working.

Talk to your healthcare provider about your result. Ask your provider:
if you need additional tests
what you can do to work toward a normal value
when you need to be tested again.

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