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.