A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood. C-reactive protein measures general levels of inflammation in your body.

High levels of CRP are caused by infections and many long-term diseases. But a CRP test cannot show where the inflammation is located or what is causing it. Other tests are needed to find the cause and location of the inflammation.

Why It Is Done

A C-reactive protein (CRP) test is done to:

• Check for infection after surgery. CRP levels normally rise within 2 to 6 hours of surgery and then go down by the third day after surgery. If CRP levels stay elevated 3 days after surgery, an infection may be present.
• Identify and keep track of infections and diseases that cause inflammation, such as:
  • Cancer of the lymph nodes (lymphoma).
  • Diseases of the immune system, such as lupus.
  • Painful swelling of the blood vessels in the head and neck (giant cell arteritis).
  • Painful swelling of the tissues that line the joints (rheumatoid arthritis).
  • Swelling and bleeding of the intestines (inflammatory bowel disease).
  • Infection of a bone (osteomyelitis).
• Check to see how well treatment is working, such as treatment for cancer or for an infection. CRP levels go up quickly and then become normal quickly if you are responding to treatment measures.

A special type of CRP test, the high-sensitivity CRP test (hs-CRP), may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. Inflammation can damage the inner lining of the arteries and make having a heart attack more likely. But the connection between high CRP levels and heart attack risk is not very well-understood.

How To Prepare

There is no special preparation for a C-reactive protein (CRP) test.

Tell your doctor all of the medicines you are taking because some medicines can affect the results.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

The health professional taking a sample of your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure on the site and then put on a bandage.