Q: The report on the blood tests for my annual physical included “C-Reactive Protein, Cardiac.” What is this?
A: C-reactive protein (CRP) is made by the liver. Elevated CRP in your blood indicates that you have inflammation or a bacterial infection. CRP levels do not always change with a viral infection.
The CRP in a healthy person is usually less than 10 milligrams per liter (mg/L). Most infections and inflammations produce CRP levels more than 100 mg/L.
CRP tests can indicate a variety of ailments including rheumatoid arthritis, pneumonia, cancer, tuberculosis, appendicitis, bacterial meningitis, inflammatory bowel disease and urinary tract infection.
The test is used to monitor patients. CRP tests don’t diagnose a specific disease; they warn that more testing may be required.
There is a high sensitivity version of the CRP test (hs-CRP) that is used to assess the risk for heart problems. It measures CRP between 0.5 and 10 mg/L. The result of this test is what you saw on the report of your blood evaluation.
Most studies show that heart attack risk rises with hs-CRP levels. If the level is lower than 1.0 mg/L, the risk is low. There’s an average risk for levels between 1.0 and 3.0 mg/L. A level higher than 3.0 mg/L indicates a high risk.
Some studies have found that if your hs-CRP level is in the upper third, your risk is twice that of someone whose level is in the lower third.
High levels of hs-CRP:
- Consistently predict new coronary events in patients who have had a heart attack.
- Are linked to lower survival rates of heart-attack victims.
- May increase the risk that an artery will reclose after it has been opened by balloon angioplasty.
- Seem to predict recurrent events in patients with peripheral arterial disease.
However, the connection between high CRP levels and heart attack risk is not completely understood. There is evidence that suggests inflammation is involved in atherosclerosis—hardening of the arteries. It’s possible that an infection might cause atherosclerosis.
There’s a theory that inflammation contributes to heart disease by working with cholesterol that is deposited in the plaques on blood-vessel walls. Inflammation may damage the plaques, allowing tiny portions to break off into the bloodstream. These small fragments can lodge in small blood vessels in the heart or brain, causing a heart attack or stroke.
The CRP test is ordered when inflammation is risky, after surgery for example. Because CRP levels drop when inflammation abates, the test is ordered to determine whether treatment of an inflammatory disease is working.
In addition, CRP tests are used to monitor the healing of wounds, organ transplants and burns.