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), or ultra-sensitive C-reactive protein (US-CRP).
A high level of CRP in the blood is a sign that there may be an inflammatory process occurring in the body. Inflammation itself isn’t typically a problem, but it can indicate a host of other health concerns, including infection, arthritis, kidney failure, and pancreatitis. High CRP levels may put patients at increased risk for coronary artery disease, which can cause a heart attack.
A CRP test is a blood test designed to measure the amount of CRP in the blood. A CRP test only needs a blood sample. Your doctor can administer a CRP test along with a cholesterol screening or other routine blood work.
Doctors don’t all agree on the implications of high CRP levels, but 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 CRP levels were more predictive of coronary conditions in women than were high cholesterol levels (a more commonly cited risk factor).
Usually, doctors order the test to determine 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. They also might use it to monitor inflammatory diseases, including:
- pelvic inflammatory disease
- inflammatory bowel disease
- autoimmune diseases, such as lupus
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 will 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
If you feel tired or dizzy after your blood test, eat a healthy snack such as fruit, juice, or nuts to help you regain energy. Reclining can also help to ease your dizziness.
A CRP test can predict 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 (greater than 10 mg/L) may indicate:
- a bone infection, or osteomyelitis
- an arthritis flare-up
- inflammatory bowel disease
- lupus or another connective tissue disease or autoimmune disease
- cancer, especially lymphoma
Note that CRP levels may also be high if you’re in the second half of pregnancy or if you’re on birth control pills.
Remember that this test doesn’t provide a complete picture of your risk for cardiovascular disease. Your doctor may order a cholesterol test, a stress test, or a coronary angiogram to further pinpoint your risk for coronary artery disease.