Overview

The level of C-reactive protein (CRP), which can be measured in your blood, increases when there's inflammation in your body. Your doctor might check your C-reactive protein level for infections or for other medical conditions.

A high-sensitivity C-reactive protein (hs-CRP) test, which is more sensitive than a standard test, also can be used to evaluate your risk of developing coronary artery disease, a condition in which the arteries of your heart are narrowed. Coronary artery disease can lead to a heart attack.

A simple blood test measures C-reactive protein.

Why it's done

Your doctor might order a CRP test to check for inflammation, which can indicate infection or a chronic inflammatory disease, such as rheumatoid arthritis or lupus, as well as risk of heart disease.

CRP tests for heart disease

It's thought that a high level of hs-CRP in your blood is associated with an increased risk of heart attacks. A CRP test doesn't indicate the cause of inflammation, though, so it's possible that a high hs-CRP level could mean there's inflammation caused by something besides your heart.

The American Heart Association doesn't recommend an hs-CRP test for everyone. Rather, the test is most useful for people who have a 5 to 10 percent chance of having a heart attack within the next 10 years. This intermediate risk level is determined by the global risk assessment, which is based on lifestyle choices, family history and current health status.

The test also helps determine the risk of a second heart attack, as people with a high level of hs-CRP who had a heart attack are more likely to have another event than those with a normal level.

People who have a low risk of having a heart attack are less likely to benefit from having an hs-CRP test. People who have a known high risk of having a heart attack should seek treatment and preventive measures regardless of how high their hs-CRP level is.

Risks

A CRP test or an hs-CRP test poses little risk. As with any blood draw, you might have some soreness or bruising around the draw site. The site can become infected, but that's rare.

How you prepare

There are no preparations for either a standard CRP test or an hs-CRP test. However, if your blood is being drawn for other tests, as well, you might need to fast or follow other instructions. Ask your doctor if you're having other tests at the same time.

Some medications can affect your CRP level. Tell your doctor about the medications you take.

What you can expect

During the procedure

Blood is drawn from a vein, usually from your arm. Before the needle is inserted, an elastic band around your upper arm causes the veins in that arm to fill with blood, and the puncture site is cleaned with antiseptic.

After the needle is inserted, a small amount of blood is collected into a vial or syringe. The band is then removed to restore circulation, and blood continues to flow into the vial. Once enough blood is collected, the needle is removed and the puncture site is covered with a pressure wrap.

This relatively painless procedure usually takes only a few minutes.

After the procedure

After your CRP test, you should be able to drive yourself home and do your normal activities.

It can take a few days to get your results. Your doctor should explain to you what the results of your test mean.

If you're having an hs-CRP test is to help find out your heart disease risk, remember that your CRP level is only one risk factor for coronary artery disease. If you have a high CRP level, it doesn't necessarily mean you're at a higher risk of developing heart disease.

Talk to your doctor about your other risk factors and ways you can try to prevent coronary artery disease and a heart attack.

Results

Your doctor will discuss what your CRP test result means.

For a standard CRP test, a normal reading is less than 10 milligram per liter (mg/L). A test result showing a CRP level greater than 10 mg/L is a sign of serious infection, trauma or chronic disease, which likely will require further testing to determine the cause.

If you're having an hs-CRP test to evaluate your risk of heart disease, current risk levels used include:

  • Lower risk. You have an hs-CRP level of less than 2.0 milligram per liter (mg/L).
  • Higher risk. You have an hs-CRP level greater than 2.0 mg/L.

These risk levels aren't a definitive measure of your risk because the ideal indicator of high CRP isn't clearly defined. Also, because a person's CRP levels vary over time, it's recommended that the average of two tests, ideally taken two weeks apart, be used to determine coronary artery disease risk.

If you're having an hs-CRP test to check for heart disease, your doctor is likely to request a cholesterol test at the same time. Other tests might be done to further evaluate your risk. Your doctor might also recommend lifestyle changes or medications to decrease your risk of a heart attack.

Clinical trials

Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this disease.

Nov. 21, 2017
References
  1. Goff DC Jr., et al. 2013 ACC/AHA guideline for assessment of cardiovascular risk: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2014;129:S49.
  2. Filippo C, et al. C-reactive protein in cardiovascular disease. https://www.uptodate.com/contents/search. Accessed Oct. 16, 2017.
  3. Morrow DA. Screening for cardiovascular disease with C-reactive protein. https://www.uptodate.com/contents/search. Accessed Oct. 16, 2017.
  4. WHO guidelines on drawing blood: Best practices in phlebotomy. World Health Organization. http://www.who.int/infection-prevention/publications/drawing_blood_best/en/. Accessed Oct. 16, 2017.
  5. Fischbach FT, et al. Immunodiagnostic studies. In: A Manual of Laboratory and Diagnostic Tests. 9th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2014.
  6. C-reactive protein, high sensitivity, serum. Mayo Medical Laboratories. https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/82047. Accessed Nov. 16, 2017.

C-reactive protein test