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An Overview of the C-reactive Protein Blood Test

written by: Dr. Kristie Leong•edited by: Diana Cooper•updated: 10/13/2010

Has your doctor ordered a C-reactive protein blood test for you? Find out what this test measures - and what the results mean.

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    If your doctor ordered a C-reactive protein blood test for you, you may be confused as to why the test was drawn and what the results mean. Below is information on the C-reactive protein test.

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    What is a C-Reactive Protein Blood Test?

    C-reactive protein, or CRP, is a protein produced by the liver that serves as a marker for inflammation. CRP levels rise when there is active inflammation somewhere in the body, but it doesn't indicate where or what's causing it.

    An elevated CRP level can come from an infection or a disease that causes inflammation such as certain types of arthritis, autoimmune diseases, tuberculosis, cancer, inflammatory bowel disease, among others. Generally, doctors order this test when they suspect one of these conditions.

    There are other situations where a doctor might order a C-reactive protein test. Since an elevated CRP level indicates inflammation, a level may be drawn to monitor the course of an infection or an inflammatory disease. For example, people who have inflammatory bowel disease frequently have an elevated CRP when they’re having an exacerbation. Drawing serial CRP levels would allow a doctor to follow the course of their disease and see if the treatment is working - since levels should go down as the inflammation subsides.

    A C-reactive protein blood test can also be used to look for a flare-up of an autoimmune or inflammatory disease.

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    Another Use for CRP Blood Tests

    A special form of C-reactive protein blood test called a hs-CRP assay is used to determine a person’s risk for heart disease since it can measure very low levels of CRP in the bloodstream. If CRP measured using this assay is above a certain level, it may indicate a higher risk for heart disease or heart attacks. In fact, CRP levels are growing favor as a test to screen for a high risk of heart disease. A high CRP level may be as important as an elevated cholesterol level for predicting a person’s future risk of heart attack.

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    What is a High CRP?

    Most inflammatory diseases and infections cause CRP levels to rise above 10 mg/dl, although any time a CRP level is rising over time, it’s concerning – even if it’s below 10 mg/dl. People who take birth control pills or hormones, are pregnant, or are obese may have slightly higher CRP levels normally, which can make the test more difficult to interpret.

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    What are the Drawbacks to Drawing a CRP Level?

    The main problem with the CRP blood test is that it’s non-specific. An elevated CRP only tells you that there’s inflammation somewhere in the body, it doesn’t pinpoint the location or the cause. A thorough clinical exam, more lab studies and other tests are required to determine why a C-reactive protein blood test is abnormal.

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    The Bottom Line

    A C-reactive protein blood test is a good screening tool for inflammation and is useful for monitoring certain diseases that cause inflammation. It’s also good for evaluating a person’s risk for heart disease. On the other hand, it’s too non-specific to make a diagnosis on its own.

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    Lab Tests Online. “C-Reactive Protein"

    Merck Manual. Eighteenth edition. 2006.

    Rev Esp Enferm Dig. 1993 Jan; 83(1):5-9.