One of the key markers for measuring heart attack risk has been elevated levels of low-density lipoprotein (LDL) cholesterol. But heart experts are now all too aware that approximately half of the people who develop coronary heart disease (CHD) actually have normal or near normal LDL cholesterol levels. What's going on? In this article from the Johns Hopkins Heart Bulletin, Dr. Roger S. Blumenthal, Director of the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, explains how C-reactive protein can predict heart disease.
If it is not always the LDL cholesterol, then what is causing the traumatic heart damage? Scientists have been searching for an explanation. It now appears that chronic inflammation of the artery walls of the heart may play an important role in triggering heart attacks.
When you injure yourself, the body's immune system revs up, jump-starting the natural healing process. It does this by creating inflammation, an all-too-familiar process that includes pain, swelling, and increased temperature. This same inflammatory response is now suspected to be a root cause of heart disease.
In the search for additional ways to predict the risk of CHD, considerable evidence indicates that a molecule called C-reactive protein (CRP) -- a protein made by the blood in response to inflammation of any kind -- tends to be elevated in people who go on to develop CHD and suffer a heart attack.
High LDL cholesterol levels lead to the buildup of fatty deposits, or plaques, within the artery walls. The plaques are infiltrated with immune cells, which may increase plaque fragility. Once the plaques become unstable, they are likely to rupture and initiate the formation of blood clots that can trigger a heart attack or stroke.
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At first, researchers thought that CRP might just be associated with other traditional risk factors for CHD, such as smoking, high blood pressure, or high LDL cholesterol levels, rather than being a causative factor in and of itself. However, research now shows that elevated CRP in the blood may directly contribute to blood vessel damage and the formation of blood clots that can cause heart attacks. Based on this and other studies, CRP appears to have predictive value that is independent of other risk factors for CHD.
Researchers now believe that the combination of a high CRP level and elevated LDL cholesterol can be particularly risky, significantly increasing the risk of heart attack and stroke.
What is CRP? The liver produces CRP when inflammation occurs anywhere in the body. Recently, researchers have found evidence that CRP is produced in the walls of blood vessels in patients who have CHD, but not in patients who do not have CHD. It is not totally clear at this point what actually causes inflammation in the heart arteries.
In the past, researchers thought that narrow the arteries were the result of too much circulating LDL cholesterol. What they are now thinking is that as the LDL begins to oxidize, the body recognizes the oxidized LDL as foreign and triggers an immune response consisting of specialized white cells (T cells and monocytes) to pull the LDL out of the inner walls of the arteries. Sometimes, this reaction causes the vessel wall to thin and become more "sticky" to platelets and other blood cells, causing an unstable plaque. Unstable plaque is itself a source of inflammation and is liable to rupture without notice, triggering a clot that can block the flow of blood, eventually leading to a heart attack.
The CRP Test -- While the CRP test is easy for doctors to perform (it involves drawing blood from a vein in the arm) and costs only about $20, we don't know exactly who really needs to be tested. To determine your personal risk level, talk to your doctor. If you are found to be at intermediate risk for a heart attack, establishing that you have a high CRP level may indicate the need to begin a more intense CHD prevention program. If you are over age 60, you may want to talk to your doctor about getting this test if the decision to treat with lifelong aspirin and statin therapy is otherwise unclear. You may also be more motivated to improve prevention efforts—such as exercising more and following a more healthful diet—if you have a high CRP or a high coronary calcium score for your age.
High-sensitivity CRP results are scored as follows:
- mg/l or lower means low risk of cardiovascular events
- 1.0 to 3.0 mg/l means moderate risk of cardiovascular events
- 3.1 mg/l and above means high risk of events
