A new study suggests that measuring the burden of coronary artery calcium (CAC) with cardiac computerized tomography (CT) appears to stratify the risk of cardiovascular disease more accurately than high-sensitivity C-reactive protein (hsCRP).

Researchers at Johns Hopkins University (JHU; Baltimore, MD, USA), the University of Miami (FL, USA), and other institutions compared coronary heart disease (CHD) and cardiovascular disease event rates after stratifying them by burden of coronary artery calcium (CAC). The study invlved 950 participants of the Multiethnic Study of Atheroslcerosis (MESA) study, with a median follow-up of 5.8 years. The researchers also calculated 5-year number needed to treat (NNT) by applying the previously recorded benefit identified in the JUPITER statin trial to the event rates within each CAC strata. The researchers also compared hsCRP with CAC for risk prediction across the range of low and high hsCRP values.

The results showed that the 444 (47%) of the patients in the MESA JUPITER population had CAC scores of 0, with the rate of CHD events at 0.8 per 1,000 person-years; conversely, 74% of all the coronary events were in the 239 (25%) participants with CAC scores of more than 100 (20.2 per 1,000 person-years). For CHD, the predicted 5-year NNT was 549 for CAC score 0, 94 for scores 1-100, and 24 for scores greater than 100. For cardiovascular disease, the NNT was 124, 54, and 19, respectively. In the total study population, presence of CAC was associated with a hazard ratio of 4.29 for CHD, and of 2.57 for cardiovascular disease; hsCRP was not associated with either disease. The study was published in the August 20, 2011, issue of the Lancet.

“CAC score could be used to target subgroups of patients who are expected to derive the most, and the least, absolute benefit from statin treatment,” concluded lead author Michael Blaha, MD, of the JHU Preventive Cardiology Center, and colleagues. “Focusing of treatment on the subset of individuals with low LDL cholesterol with measurable atherosclerosis might represent a more appropriate allocation of resources, reduce overall healthcare cost, and prevent the occurrence of a similar number of events.”

The researchers acknowledged that CAC scoring has both advantages and disadvantages when compared with hsCRP. Advantages of CAC scoring include the fact that it is a direct measure of the burden of atherosclerosis, it has small variability on repeated testing, and it has consistent thresholds of risk in different populations, while thresholds for hsCRP vary by sex and ethnic origin. Disadvantages include radiation exposure, a risk of incidental findings leading to further imaging, and a higher cost compared with hsCRP.

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