As of Thursday, January 9, 2014
DEAR DOCTOR K: A few years ago my doctor told me that C-reactive protein was an important indicator of heart disease risk. At my last checkup, he didn’t mention it at all. Is it still considered important?
DEAR READER: C-reactive protein (CRP) is produced by the liver in response to inflammation anywhere in the body. Inflammation contributes to atherosclerosis, the buildup of fatty deposits in blood vessel walls that’s responsible for most heart attacks and many strokes. CRP from inflamed plaques of atherosclerosis spills into the blood.
Inflammation not only makes plaques of atherosclerosis grow faster; inflammation inside the plaques also makes them more likely to rupture. When even a small plaque ruptures, it can quickly cause a blood clot that suddenly stops the flow of blood to one part of the heart. That can cause a heart attack.
CRP isn’t dangerous in and of itself. Rather, it’s a sign of inflammation in the body. A new test, called the high-sensitivity CRP (hsCRP) test, measures inflammation of the blood vessels.
In the interests of full transparency, I need to tell you that the use of this test to help determine a person’s risk of getting heart disease was pioneered at my hospital. The hospital gets some royalties from the use of the test. (I don’t get any money from its use.)
People with the highest CRP levels are about twice as likely to suffer a heart attack or other cardiac event as people with the lowest levels. That’s why CRP is used, along with other risk factors (such as cholesterol and blood pressure), to estimate cardiovascular risk.
Your doctor may have been silent on the subject because the standards for using CRP are still evolving. For example, we don’t know what CRP target levels should be for men and women of different racial and ethnic groups. For now, risk assessment is based on the following CRP levels:
— below 1 mg/L = low risk
— 1-3 mg/L = average risk
— above 3 mg/L = high risk
If you are already considered high risk for heart disease or are being treated for it, a CRP test is not necessary. The results won’t change how your condition is managed.
If you have a moderate risk of heart attack, an hsCRP test might help to more accurately place you in a high- or low-risk category. For example, if you are at moderate risk based on high cholesterol, you might move into the high-risk category if you also have elevated CRP. The result might be more aggressive treatment.
If you have other risk factors, such as diabetes or high blood pressure, ask your doctor about an hsCRP test. It might help to better assess your risk.
Like most issues in medicine, there is controversy about the value of measuring the hsCRP level in the blood. Some doctors think that it does not add important new information in calculating risk. As I look at the evidence, I think it is valuable.
Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.