Accordingly, the USPSTF recently conducted several systematic reviews to evaluate the usefulness of nine of the most commonly promoted "emerging" cardiovascular risk factors. They concluded that there is insufficient evidence to support routinely using any of them.
The nine risk factors which were evaluated and found wanting were:
- C-reactive protein (CRP)
- Coronary artery calcium scores
- lipoprotein (a) level
- homocysteine level
- white blood cell count
- fasting blood glucose
- periodontal disease
- ankle-brachial index (a measure of the difference in blood pressure between the arm and the leg, which can be an indicator of disease in the leg arteries)
- carotid intima-media thickness (CIMT, an ultrasound test measuring the "thickness" of the wall of the carotid artery, thought to reflect one's "burden" of atherosclerosis)
In conducting its assessment, the USPSTF noted that the tried-and-true Framingham index remains the gold standard for estimating your cardiac risk. The Framingham index uses your age, gender, cholesterol values, smoking history and blood pressure to compute your risk of either having a heart attack or dying from heart disease over the next 10 years. (Use this on-line calculator to compute your Framingham risk score.) A risk of less than 10% is considered "low," above 20% is considered "high," and between 10-20% is considered "intermediate."
There is good evidence that aggressive treatment can improve the outcome of patients with "high" Framingham scores, but little hard evidence that aggressive treatment helps those with intermediate scores. (People with low Framingham scores simply do not need aggressive treatment.) Accordingly, in order to have any practical value, emerging risk factors (such as the nine listed above) would need to be able to re-classify a substantial proportion of people with intermediate risk into the high risk category. (Unless such a re-classification were accomplished, measuring the emerging risk factor would have no impact on the need for therapy.)
Simply put, the USPSTF analysis failed to show that any of these nine risk factors had any reliable, measurable impact on the 10-year risk as provided by the Framingham score. In other words, once you have your Framingham score, none of these newer risk factors are likely to give you any useful additional information.
The USPSTF study is likely to prove controversial, especially since its findings contradict at least some of the conventional wisdom held dear by modern cardiologists. (Consider, for instance, that the American College of Cardiology and American Heart Association guideline committee in 2007 advised that measuring coronary artery calcium scores could often be helpful in people with intermediate risk. But in its study, the USPSTF specifically noted that it tried but could not identify the evidence used by that guideline committee to support its recommendation.)
What This Means To You
Let the experts fight out the details. It will take years, or even longer. Academics get paid for being, well, academic. Hot scientific controversies are seldom actually settled, because once they are, the paid experts would have to find something else to do.In the meantime, estimate your own risk for cardiac disease. You can do this using the formal Framingham score, or more simply, by having a look at this article on risk assessment. If you find yourself in the "high risk" category, see your doctor. If you are in the "intermediate risk" category, do everything you can to reduce your cardiac risk factors - keep in mind that moving yourself back to a low-risk category is often within your control.
Sources:
Helfand M, Buckley DI, Freeman M, et al. Emerging Risk Factors for Coronary Heart Disease: A Summary of Systematic Reviews Conducted for the U.S. Preventive Services Task Force. Ann Int Med. 2009;151:496-507.
Greenland P, Bonow RO, Brundage BH, et al. American College of Cardiology Foundation Clinical Expert Consensus Task Force (ACCF/AHA Writing Committee to Update the 2000 Expert Consensus Document on Electron Beam Computed Tomography). ACCF/AHA 2007 clinical expert consensus document on coronary artery calcium scoring by computed tomography in global cardiovascular risk assessment and in evaluation of patients with chest pain: a report of the American College of Cardiology Foundation Clinical Expert Consensus Task Force (ACCF/AHA Writing Committee to Update the 2000 Expert Consensus Document on Electron Beam Computed Tomography). Circulation. 2007;115:402-26.
