C-reactive protein test

Overview

C-reactive protein (CRP) is a protein made by the liver. The level of CRP increases when there's inflammation in the body. A simple blood test can check your C-reactive protein level.

A high-sensitivity C-reactive protein (hs-CRP) test is more sensitive than a standard C-reactive protein test. That means the high-sensitivity test can find smaller increases in C-reactive protein than a standard test can.

The hs-CRP test can help show the risk of getting coronary artery disease. In coronary artery disease, the arteries of the heart narrow. Narrowed arteries can lead to a heart attack.

Why it's done

Your health care provider might order a C-reactive protein test to:

• Check for infection.
• Help diagnose a chronic inflammatory disease, such as rheumatoid arthritis or lupus.
• Learn your risk of heart disease.
• Learn your the risk of a second heart attack.

A note about CRP tests for heart disease

A high level of hs-CRP in the blood has been linked to an increased risk of heart attacks. Also, people who have had a heart attack are more likely to have another heart attack if they have a high hs-CRP level. But their risk goes down when their hs-CRP level is in the typical range.

An hs-CRP test isn't for everyone. The test doesn't show the cause of inflammation. So it's possible to have a high hs-CRP level without it affecting the heart.

An hs-CRP test may be most useful for people who have a 10% to 20% chance of having a heart attack within the next 10 years. This is known as intermediate risk. A health care provider can determine your risk using tests that look at your lifestyle choices, family history and overall health.

How you prepare

Hard exercise, such as intense weight training or a long run, can cause a sudden jump in the C-reactive protein level. Your health care provider might ask you to avoid such activities before the test.

Some medicines can affect CRP level. Tell your care provider about the medicines you take, including those you bought without a prescription.

If your blood sample will be used for other tests, you may need to avoid food or drink for a period before the test. For example, if you're having an hs-CRP test to check for heart disease, you might have a cholesterol test, which requires fasting, at the same time.

Your health care provider tells you how to prepare for your test.

What you can expect

To take a sample of your blood, a health care provider places a needle into a vein in your arm, usually at the bend of the elbow. The blood sample goes to a lab for analysis. You can return to your usual activities right away.

Results

It can take a few days to get results. Your health care provider can explain what the test results mean.

C-reactive protein is measured in milligrams per liter (mg/L). Results equal to or greater than 8 mg/L or 10 mg/L are considered high. Range values vary depending on the lab doing the test.

A high test result is a sign of inflammation. It may be due to serious infection, injury or chronic disease. Your health care provider may recommend other tests to determine the cause.

Results for an hs-CRP test are usually given as follows:

• Lower risk of heart disease: Less than 2.0 mg/L
• Higher risk of heart disease: Equal to or greater than 2.0 mg/L

A person's CRP levels vary over time. A coronary artery disease risk assessment should be based on the average of two hs-CRP tests. It's best if they're taken two weeks apart. Values above 2.0 mg/L may mean an increased risk of heart attacks or risk of a repeat heart attack.

Hs-CRP level is only one risk factor for coronary artery disease. Having a high hs-CRP level doesn't always mean a higher risk of developing heart disease. Other tests results can help determine the risk.

Talk to your health care provider about your risk factors for heart disease and ways to try to prevent it. Lifestyle changes or medicines might help lower the risk of a heart attack.