C-reactive protein (CRP) is a substance produced by the liver in response to inflammation. Other names for CRP are high-sensitivity C-reactive protein (hs-CRP) and ultra-sensitive C-reactive protein (us-CRP).
A high level of CRP in the blood is a marker of any condition that causes inflammation, from an upper respiratory infection to cancer. High CRP levels can indicate that there is inflammation in the arteries of the heart, which can mean a higher risk for heart attack. It is important to remember, however, that CRP is an extremely nonspecific test and can be elevated in any inflammatory condition.
Doctors don’t all agree on the implications of high CRP levels. Some believe there’s a correlation between high CRP levels and an increased likelihood for heart attack or stroke.
The Physicians’ Health Study found that among nearly 15,000 healthy adult men, a high level of CRP was associated with a risk of heart attack that was three times higher than average. According to the Cleveland Clinic, the Harvard Women’s Health Study showed that high CRP levels were more predictive of coronary conditions in women than were high cholesterol levels. High cholesterol is a more commonly cited risk factor.The Jackson Heart Study found that hs-CRP is associated with type 2 diabetes in African-Americans.
Doctors may order this test in conjunction with other tests to assess a person’s risk for heart disease or stroke. Doctors may also order a CRP test after surgery to check for signs of postsurgical infection or to monitor inflammatory diseases, including:
- inflammatory bowel disease
- inflammatory arthritis such as rheumatoid
- autoimmune diseases, such as lupus
According to the Mayo Clinic, the American Heart Association does not recommend the test for general screening of heart disease. If you are one of the 47 percent of Americans with risk factors for heart disease, CRP test results might help you better monitor your heart health. The Centers for Disease Control and Prevention (CDC) consider high blood pressure, high cholesterol, and smoking as big risk factors for heart disease. If you have a family history of heart disease, you are also at high risk.
No special preparation is necessary for this test. You may eat normally on the day of the test. A nurse or other health practitioner will draw blood from a vein, usually on the inside of your elbow or the back of your hand.
First, they will clean the skin over the vein with antiseptic. Next, they’ll wrap an elastic band around your arm, causing your veins to bulge out slightly. Then, the practitioner will insert a small needle into the vein and collect your blood in a sterile vial.
After the nurse or health practitioner collects your blood sample, they will remove the elastic band around your arm and ask you to apply pressure to the puncture site with gauze. They may use tape or a bandage to hold the gauze in place.
This is a routine test with low risk, but there’s a slight chance of the following complications from the blood draw:
- excessive bleeding
- dizziness or lightheadedness
- bruising or infection at the puncture site
A CRP test can be helpful in assessing a patient’s risk of heart disease, especially in combination with high cholesterol levels. The benefits of this test outweigh potential complications, especially for those at risk for heart disease or stroke and those recovering from recent surgery.
C-reactive protein is measured in milligrams of CRP per liter of blood (mg/L). In general, a low C-reactive protein level is better than a high one, because it indicates less inflammation in the body.
According to the Cleveland Clinic, a reading of less than 1 mg/L indicates you’re at low risk of cardiovascular disease. A reading between 1 and 2.9 mg/L means you’re at intermediate risk. A reading greater than 3 mg/L means you’re at high risk for cardiovascular disease. A reading above 10 mg/L may indicate a need for further testing to determine the cause of severe inflammation in your body.
An especially high CRP reading of greater than 10 mg/L may indicate:
- a bone infection, or osteomyelitis
- an arthritis flare-up
- inflammatory bowel disease
- lupus, another connective tissue disease, or another autoimmune disease
- cancer, especially lymphoma
Note that CRP levels may also be high if you’re on birth control pills or in the second half of pregnancy. Low-grade inflammation levels can be increased by both oral contraceptives and the increased blood flow that begins midway through the second trimester of pregnancy.
If you are pregnant or have any other chronic infection or inflammatory disease, a CRP test is unlikely to accurately assess your risk for heart disease. Before having a CRP test, speak to your doctor about any medical conditions that may skew the test results. Since there are other blood tests that can be performed instead, you might wish to forego a CRP test altogether.
Remember that this test doesn’t provide a complete picture of your risk for cardiovascular disease. Your doctor will consider your lifestyle risk factors and family history when determining which follow-up tests are best for you. He or she may also order tests such as an EKG, echocardiogram, stress test, CT scan of the coronary arteries, or heart catheterization.
Lowering your CRP is not a guaranteed way to lower your risk of cardiovascular, kidney, or autoimmune disease. It’s important to know that high CRP is what doctors call a “biomarker.” A biomarker is a factor to keep in mind when analyzing a person’s health, but not a standalone indicator of a particular diagnosis.
A new review of the medical literature indicates that a healthy dietary pattern resulted in lowered CRP levels. The Mediterranean diet and the Nordic diet were both linked to a decrease in CRP. If you are at risk for heart disease, pursuing a healthy diet that works for you should be part of your lifestyle regardless.
If you are at high risk for cardiovascular disease and your test results show high CRP, your doctor may suggest a statin or other cholesterol-lowering medication. An aspirin regimen may be recommended as well. Vitamin C has also been explored as an effective treatment to lower CRP levels for people that are at an elevated risk for cardiovascular disease.