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What is C-reactive protein?
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 inflammation. It can be caused by a wide variety of conditions, from infection to cancer.
High CRP levels can also indicate that there’s inflammation in the arteries of the heart, which can mean a higher risk of heart attack. However, the CRP test is an extremely nonspecific test, and CRP levels can be elevated in any inflammatory condition.
The Physicians’ Health Study found that among healthy adult men, those with a high level of CRP were three times more likely to have a heart attack than those with low levels of CRP. This was among men who had no previous history of heart disease.
According to the Cleveland Clinic, the Harvard Women’s Health Study showed that high CRP levels were more predictive of coronary conditions and stroke in women than were high cholesterol levels.
Doctors may order this test in conjunction with other tests to assess a person’s risk of heart disease or stroke. There is also new research that suggests CRP may be used as a predictor in health outcomes related to chronic obstructive pulmonary disease (COPD). Doctors may also order a CRP test to diagnose inflammatory autoimmune diseases, including:
Expert opinion from the American Heart Association in 2013 states that when considering all risk factors, individuals with CRP levels greater than or equal to 2 milligrams per liter (mg/L) likely need more intense management and treatment for heart disease.
Elevated levels of CRP may have an important role in identifying those who might need closer follow-up or more intensive treatment after heart attacks or heart procedures.
CRP levels may also be useful in uncovering those at risk of heart disease where cholesterol levels alone may not be helpful.
- high blood pressure
- high cholesterol
- unhealthful diet
- limited physical activity
- alcohol use in excess
- being overweight
A family history of heart disease also puts you at higher risk of heart disease.
No special preparation is necessary for this test. You may eat normally on the day of the test.
A nurse or other health practitioner draws blood from a vein, usually on the inside of your elbow or the back of your hand:
First, they clean the skin over the vein with antiseptic. Next, they wrap an elastic band around your arm, causing your veins to bulge out slightly. The practitioner then inserts a small needle into the vein and collects your blood in a sterile vial.
After the nurse or health practitioner collects your blood sample, they 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:
A CRP test can be helpful in assessing a person’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 of heart disease or stroke and those recovering from recent heart procedures.
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 of cardiovascular disease.
A reading above 10 mg/L may signal a need for further testing to determine the cause of such significant inflammation in your body. This especially high reading may indicate:
- a bone infection, or osteomyelitis
- an autoimmune arthritis flare-up
- lupus, connective tissue disease, or other autoimmune diseases
- cancer, especially lymphoma
- pneumonia or other significant infection
Elevated CRP values in pregnancy may be a marker for complications, but more studies are necessary to fully understand the role of CRP and pregnancy.
If you’re pregnant or have any other chronic infection or inflammatory disease, a CRP test is unlikely to accurately assess your risk of 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 of cardiovascular disease. Your doctor will consider your lifestyle risk factors, other medical conditions, and family history when determining which follow-up tests are best for you.
They may also order one of the following tests:
Lowering your CRP isn’t a guaranteed way to lower your risk of cardiovascular 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 stand-alone indicator of a particular diagnosis.
Research indicates that a healthy dietary pattern can lower CRP levels. The Mediterranean diet has been consistently shown to lower CRP levels. If you’re at risk of heart disease, pursuing a healthy diet that works for you should be part of your lifestyle regardless.
If you’re at high risk of 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 a way to lower CRP levels for people that are at an elevated risk of cardiovascular disease.