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C-reactive protein

CRP; High-sensitivity C-reactive protein; hs-CRP

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.

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Blood test

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How the Test is Performed

A blood sample is needed. This is most often taken from a vein. The procedure is called a venipuncture.

How to Prepare for the Test

No special steps are needed to prepare for this test.

How the Test will Feel

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.

Why the Test is Performed

The CRP test is a general test to check for inflammation in the body. It is not a specific test. That 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:

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.

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 Results

Normal CRP values vary from lab to lab. Generally, there are low levels of CRP detectable in the blood. The levels often increase slightly with age, female gender and in African Americans.

Increased serum CRP is related to traditional cardiovascular risk factors and may reflect the role of these risk factors in causing vascular inflammation.

According to the American Heart Association, results of the hs-CRP in determining the risk for heart disease can be interpreted as follows:

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.

What Abnormal Results Mean

A positive test means you have inflammation in the body. This may be due to a variety of conditions, including:

This list is not all inclusive.

Note: Positive CRP results also occur during the last half of pregnancy or with the use of birth control pills (oral contraceptives).

Risks

Risks associated with having blood drawn are slight, but may include:

Related Information

Acute
Complement
Rheumatoid arthritis
Rheumatic fever
Cancer
Pulmonary tuberculosis
Pneumonia - adults (community acquired)
Heart attack
Systemic lupus erythematosus

References

Chernecky CC, Berger BJ. C. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:266-432.

Dietzen DJ. Amino acids, peptides, and proteins. In: Rifai N, ed. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. St Louis, MO: Elsevier; 2018:chap 28.

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.

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Review Date: 1/10/2019  

Reviewed By: Gordon A. Starkebaum, MD, MACR, ABIM Board Certified in Rheumatology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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