The C-reactive protein (CRP) blood test is a medical test that measures the level of CRP in a sample of your blood. CRP is a protein that your liver makes, and its level increases when there is inflammation in your body. The test can show whether you have inflammation in your body and how much, but it cannot show what is causing the inflammation or which part of your body is inflamed. The CRP test is used to help find or monitor inflammation in acute or chronic conditions, including infections from bacteria or viruses, inflammatory bowel disease, autoimmune disorders, such as lupus, rheumatoid arthritis, and vasculitis, and lung diseases, such as asthma. The test can also be used to see if treatments for chronic inflammation are working or to make treatment decisions if you have sepsis, which is a life-threatening medical emergency.
There are two types of CRP tests: a standard CRP test and a high-sensitivity CRP (hs-CRP) test. The hs-CRP test is more sensitive than the standard CRP test and can find smaller increases in CRP than a standard test can. The hs-CRP test can help show the risk of getting coronary artery disease, which is a condition where the arteries of the heart narrow and can lead to a heart attack. A high level of hs-CRP in the blood has been linked to an increased risk of heart attacks, and people who have had a heart attack are more likely to have another heart attack if they have a high hs-CRP level.
To perform the CRP test, a healthcare provider takes a blood sample, usually from a vein, and sends it to a lab where a medical laboratory scientist prepares the samples and performs the test on machines known as analyzers. The test results are usually given as milligrams per deciliter (mg/dL) . Normal CRP values vary from lab to lab, and the levels often increase slightly with age, female sex, and in African Americans. A positive test means you have inflammation in your body, but it cannot pinpoint the exact location or reason. Your healthcare provider may recommend other tests to determine the cause of the inflammation.
