C-reactive protein (CRP) is a substance produced by the liver in response to inflammation. C-reactive protein is also called high-sensitivity C-reactive protein, which may be shortened to HS-CRP, US-CRP, or simply CRP.
If high levels of CRP are present in the blood, this is a sign that there may be inflammation in the body. Inflammation while non-specific itself can indicate a host of other health concerns, including asymptomatic infection, arthritis, kidney failure, and pancreatitis, to name a few. 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.. Because it requires only a blood draw, a CRP test can be administered along with a cholesterol screening or other routine blood work.
Physicians do not all agree on the implications of high CRP levels, but some believe there is a correlation between high CRP levels and heart attack or stroke. In one clinical study of 18,000 healthy adults, a high level of CRP was associated with a risk of heart attack three times higher than average. Another study that focused on women showed that CRP levels were more predictive of coronary conditions than were high cholesterol levels (a more commonly cited risk factor).
Usually, the test is ordered to determine a person’s risk for heart disease or stroke. Physicians may also order a CRP test after surgery to check for signs of post-surgical infection. Additionally, they might use it to monitor a number of inflammatory diseases, including:
- pelvic inflammatory disease
- inflammatory bowel disease
- diseases of the immune system, such as lupus
No special preparation is required, and you may eat normally on the day of the test. To administer the test, a nurse or other health practitioner will draw blood from a vein, usually one on the inside of your elbow or the back of your hand.
First, the skin over the vein will be cleaned with antiseptic. Next, the nurse or health practitioner will 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.
Once your blood sample has been collected, the elastic band will be removed and you’ll be asked to apply pressure to the puncture site with gauze. Tape or a bandage may be used to hold the gauze in place.
This is a routine and low-risk test, but there is 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 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 who have undergone 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 a low risk of cardiovascular disease. A reading between 1 and 2.9 mg/L denotes intermediate risk. A reading greater than 3 mg/L means you are 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. (Cleveland Clinic)
An especially high CRP reading (greater than 10 mg/L) may indicate:
- an infection
- an arthritis flare-up
- inflammatory bowel disease
- lupus or other connective tissue/immune disease
Note that CRP levels may also be high during the second half of pregnancy or in patients on birth control pills.
Remember that this test does NOT 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.