The level of C-reactive protein (CRP), which can be measured in your blood, increases when there's inflammation in your body. Your doctor may check your C-reactive protein level treatment 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 eventually lead to a heart attack.
A simple blood test measures C-reactive protein. Some researchers think that treating people with high C-reactive protein levels will lessen their risk of heart attack or stroke.
However, according to the American Heart Association, this test isn't recommended for general screening for heart disease. And it might not be helpful in determining your heart attack risk, depending on your health and lifestyle choices.
Your doctor may order a CRP test to check for inflammation. Inflammation may 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 high hs-CRP levels in your blood are associated with narrowed coronary arteries. A CRP test can't tell your doctor where the inflammation is, though, so it's possible that a high hs-CRP level could mean there's inflammation somewhere other than your heart.
According to the American Heart Association, an hs-CRP test is most useful for people who have an intermediate risk (a 10 to 20 percent chance) of having a heart attack within the next 10 years. This risk level, called the global risk assessment, is based on lifestyle choices, family history and current health status.
People who have a low risk of having a heart attack are less likely to benefit from having an hs-CRP test, and people who have a high risk of having a heart attack should seek treatment and preventive measures regardless of how high their hs-CRP level is.
An hs-CRP test poses little risk. For any blood draw, you may have some soreness or tenderness around the draw site, and rarely, the site may become infected.
There are no special 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 may 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 any medications you take.
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 will likely take 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 may take a few days for you to get your results back. Your doctor should explain to you what the results of your test mean.
If you're having an hs-CRP test to help find out your heart disease risk, keep in mind that your CRP level is only one risk factor for coronary artery disease. If your test result shows 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.
Your doctor will discuss what your CRP test result means.
If you're having an hs-CRP test to evaluate your risk of heart disease, these are the current risk levels used:
- Low risk. You have a CRP level of less than 1.0 milligram per liter (mg/L).
- Average risk. You have a CRP level between 1.0 and 3.0 mg/L.
- High risk. You have a CRP level greater than 3.0 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 coronary artery disease risk. Your doctor may also recommend lifestyle changes or medications to decrease your risk of a heart attack.
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.
Dec. 12, 2014
- Greenland P, et al. ACCF/AHA guideline for assessment of cardiovascular risk in asymptomatic adults: A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2010;122:e584.
- Morrow DA. C-reactive protein in cardiovascular disease. http://www.uptodate.com/home. Accessed Oct. 19, 2014.
- Morrow DA. Screening for cardiovascular disease with C-reactive protein. http://www.uptodate.com/home. Accessed Oct. 19, 2014.
- McKean SC, et al. Principles and Practice of Hospital Medicine. New York, N.Y: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=749. Accessed Oct. 19, 2014.
- WHO guidelines on drawing blood: Best practices in phlebotomy. World Health Organization. http://whqlibdoc.who.int/publications/2010/9789241599221_eng.pdf. Accessed Oct. 19, 2014.