Heart Calcium Scans Sharpen Risk Mainly for Borderline Patients, Study Finds

Coronary artery calcium (CAC) scans, a CT test measuring calcium buildup in heart arteries, are becoming popular for gauging heart disease risk. A new Northwestern Medicine study suggests the scan helps a narrower group of patients than assumed. Researchers followed more than 6,000 adults for 10 years and found that adding a calcium score improved on PREVENT, the American Heart Association's risk calculator, only slightly.

PREVENT estimates 10- or 30-year cardiovascular risk from blood pressure, cholesterol, age and sex; the CAC scan looks for calcium plaque in the coronary arteries, where higher scores are generally associated with greater risk. In the Multi-Ethnic Study of Atherosclerosis, researchers tracked adults ages 45 to 79 who had both scores; over the next decade, 6% had a heart attack or stroke. Discrimination -- how well the model predicts future events -- rose only from 0.73 with PREVENT alone to 0.75 with calcium scores added.

The picture changed for people in PREVENT's borderline or intermediate category (a 3% to 9% estimated 10-year risk), where the calcium score gave a more meaningful improvement. "For patients at borderline risk, knowing their calcium score can help determine whether their risk is actually lower or higher than initially estimated, which can help guide treatment decisions," said Dr. Nilay Shah, the study's senior author and assistant professor of medicine in the division of cardiology at Northwestern University Feinberg School of Medicine.

Shah said scanning low-risk people "may result in unnecessary radiation exposure, testing and costs with unclear clinical benefits," while high-risk patients face unnecessary testing, since they are recommended to start a statin regardless of what the scan shows.

About 10% of U.S. adults ages 30 to 79 have cardiovascular disease, the nation's leading cause of death. The study, published Aug. 26 in JAMA, said further research is needed on whether calcium scores help in higher-risk groups such as South Asian and Filipino adults, and in people younger than 45.