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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:
- 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.
How To Prepare
There is no special preparation for a C-reactive protein (CRP) test. You might be asked to not eat or drink for a few hours before the 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 .
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.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Results are usually available within 24 hours.
Any condition that results in sudden or severe inflammation may increase your CRP levels.
Some medicines may decrease your CRP levels.
Many conditions can change CRP levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.
What Affects the Test
You may not be able to have the test, or the results may not be helpful, if:
What To Think About
C-reactive protein can be found with this test within a few hours of an inflammation response. So a higher-than-normal CRP level shows a current inflammation. The CRP level drops back to normal when the inflammation goes away.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Current as of:
August 31, 2020
Author: Healthwise Staff
Adam Husney MD - Family Medicine
Brian D. O'Brien MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
Stephen Fort MD, MRCP, FRCPC - Interventional Cardiology
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