C-reactive protein (CRP) is produced by the liver. The level of CRP rises when there is inflammation throughout the body. It is one of a group of proteins, called acute phase reactants, that go up in response to inflammation. The levels of acute phase reactants increase in response to certain inflammatory proteins called cytokines. These proteins are produced by white blood cells during inflammation.
This article discusses the blood test done to measure the amount of CRP in your blood.
Acute phase reactants - CRP
A blood sample is needed. This is most often taken from a vein. The procedure is called a venipuncture.
No special steps are needed to prepare for this test.
When the needle is inserted to draw blood, some people feel moderate pain. Others may feel only a prick or stinging sensation. Afterward, there may be some throbbing.
The CRP test is a general test to check for inflammation in the body. It is not a specific test. This means it can reveal that you have inflammation somewhere in your body, but it cannot pinpoint the exact location. The CRP test is often done with the ESR or sedimentation rate test which also looks for inflammation.
You may have this test to:
A more sensitive CRP test, called a high-sensitivity C-reactive protein (hs-CRP) assay, is available to determine a person's risk for heart disease.
Normal CRP values vary from lab to lab. The levels often increase slightly with age, female sex and in African Americans. The majority of healthy adults have levels less than 0.3 mg/dL.
However, a low CRP level does not always mean that there is no inflammation present. Levels of CRP may not be increased in people with rheumatoid arthritis and lupus. The reason for this is unknown.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
It is unclear if a minor rise of 0.3 to 1 mg/dL in CRP levels is a cause for concern. The hs-CRP is more precise and may be used to further understand these results.
A positive test means you have inflammation in the body. The cause of a high CRP cannot always be determined. Some include:
According to the American Heart Association, results of the hs-CRP can be interpreted as follows:
Note: Positive CRP results also occur during the last half of pregnancy or with the use of birth control pills (oral contraceptives).
Risks associated with having blood drawn are slight, but may include:
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Haberman R, Fors Nieves CE, Cronstein BN, Saxena A. Acute phase reactants. In: Firestein GS, Budd RC, Gabriel SE, Koretzky GA, McInnes IB, O’Dell JR, eds. Firestein & Kelley's Textbook of Rheumatology. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 60.
Ridker PM, Libby P, Buring JE. Risk markers and the primary prevention of cardiovascular disease. In: Zipes DP, Libby P, Bonow RO, Mann DL, Tomaselli GF, Braunwald E, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 11th ed. Philadelphia, PA: Elsevier; 2019:chap 45.
Reviewed By: Diane M. Horowitz, MD, Rheumatology and Internal Medicine, Northwell Health, Great Neck, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.