C-reactive protein test

Date Updated: 06/25/2021

Overview

The level of C-reactive protein (CRP) increases when there's inflammation in your body. A simple blood test can be done to check your C-reactive protein level.

A high-sensitivity C-reactive protein (hs-CRP) test is more sensitive than a standard CRP test. That means the high-sensitivity test can detect slight increases within the normal range of standard CRP levels. The hs-CRP test can be used to determine 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.

Why it's done

Your doctor might order a CRP test to:

Check for inflammation due to an infection
Help diagnose a chronic inflammatory disease, such as rheumatoid arthritis or lupus
Determine your risk of heart disease
Evaluate your 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 with a high level of hs-CRP who have had a heart attack are more likely to have another one compared with those with a normal hs-CRP level.

An hs-CRP test isn't recommended for everyone. The test doesn't show the cause of inflammation — and it's possible that a high level could mean the inflammation isn't affecting your heart, especially if the level is significantly higher than normal.

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, or intermediate risk. Your doctor will determine your risk level using assessment scoring tests that consider your lifestyle choices, family history and current health status.

If you're at high risk of having a heart attack, you should always get treatment and take steps to protect your heart health, regardless of your hs-CRP level.

How you prepare

Very strenuous exercise, such as intense weight training or a very long run, can cause sudden increases in your CRP level. Your doctor may tell you to avoid such activities before your test.

If your blood sample will be used for additional tests, you may need to avoid eating or drinking for a certain amount of time before the test. For example, if you're having an hs-CRP test to check for heart disease, your doctor is likely to order a cholesterol test at the same time.

Your doctor or nurse will give you specific instructions on how to prepare for your test.

Some medications can affect your CRP level. Always tell your doctor about the medications you take, including those bought without a prescription.

What you can expect

To take a sample of your blood, a member of your health care team will insert a needle into a vein in your arm, usually at the bend in your elbow. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.

Results

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

CRP is measured in milligrams per liter (mg/L). Results for a standard CRP test are usually given as follows:

Normal: Less than 10 mg/L
High: Equal to or greater than 10 mg/L

Note: Abnormal range values may vary depending on the laboratory doing the test. A high CRP test result is a sign of acute inflammation. It may be due to serious infection, injury or chronic disease. Your doctor will recommend other tests to determine the cause.

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

Lower risk of heart disease: hs-CRP level less than 2.0 mg/L
Higher risk of heart disease: hs-CRP level 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, ideally taken two weeks apart. Values above 2.0 mg/L may reflect an increased risk of heart attacks or risk of a recurrent heart attack.

Remember that your hs-CRP level is only one risk factor for coronary artery disease. If you have a high hs-CRP level, it doesn't definitely mean you have an overall higher risk of developing heart disease. Other tests need to be done to further evaluate your risk.

Talk to your doctor about all your risk factors and ways you can try to prevent coronary artery disease and a heart attack. Your doctor might recommend lifestyle changes or medications to decrease your risk of a heart attack.