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.
When to do CRP test?
Doctors may refer to 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). High cholesterol is a more commonly cited risk factor. hs-CRP may play a role in the development of type 2 diabetes. Doctors may also order a CRP test to diagnose inflammatory autoimmune diseases, including:
- inflammatory bowel disease (IBD)
- rheumatoid arthritis
CRP and 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.
Doctors consider these conditions significant risk factors for developing heart disease:
- 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.
Normal levels of CRP or C-reactive protein
C-reactive protein is measured in milligrams of CRP per litre 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.
- 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.
Note: result varies on measuring units. Please check local laboratory measuring units.
High C-reactive protein 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
CRP or C-reactive protein with other health conditions
Learn: Insulin test
Note that CRP levels may also be elevated for those taking birth control pills. However, other markers of inflammation aren’t necessarily abnormal in these individuals.
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:
- electrocardiogram (ECG)
- echocardiogram (2D ECHO)
- stress test
- CT scan of the coronary arteries
- heart catheterization
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