Coronary artery calcium scans provide the most clinical value for patients sitting in the middle of the cardiovascular risk range, according to a Northwestern Medicine study examining patient data over a decade. While the fast and inexpensive imaging tests can detect hidden plaque before symptoms appear, researchers found they offer limited additional benefit for adults already categorized as very low risk or high risk.
How Coronary Artery Calcium Scans Work
Heart attacks and strokes frequently develop after years of silent changes in blood vessels. Cholesterol and other materials accumulate in artery walls to form plaque, a process known as atherosclerosis, which eventually becomes calcified in some patients. According to Northwestern Medicine researchers, a coronary artery calcium scan uses a low-dose CT scan to detect this calcium in the arteries supplying blood to the heart. The resulting measurement is reported as a calcium score, where a score of zero indicates no calcified plaque was detected, while higher scores point to a greater burden of coronary atherosclerosis and an increased future risk of cardiovascular events.
Evaluating Risk with the PREVENT Calculator
Before ordering imaging tests, physicians often rely on mathematical risk estimation tools. The American Heart Association developed the PREVENT calculator to estimate cardiovascular risk using common health information that does not require imaging. According to the study data, PREVENT evaluates factors such as age, sex, cholesterol levels, and blood pressure to help doctors discuss lifestyle changes and preventive medications like statins with patients.
To determine how much value imaging adds, the Northwestern team analyzed data from more than 6,000 adults aged 45 to 79 who participated in the Multi-Ethnic Study of Atherosclerosis. Each participant had a baseline coronary calcium score and sufficient health data for a PREVENT risk estimate, allowing researchers to track outcomes over a 10-year period during which about 6% of participants experienced a heart attack or stroke.
Why Intermediate Risk Groups Benefit Most
When researchers compared predictions against actual 10-year outcomes, the overall statistical improvement was modest. A measure of prediction accuracy rose from 0.73 using the PREVENT tool alone to 0.75 when coronary calcium information was included. However, a deeper analysis across different risk brackets showed that calcium scores made a substantial difference for individuals classified as having borderline or intermediate cardiovascular risk.
According to the study findings, these participants had an estimated 10-year risk between 3% and 9%. That specific window often creates clinical uncertainty because patients may not clearly require medication yet possess enough risk to warrant preventive measures. A positive calcium score can give physicians stronger evidence that preventive treatment is worthwhile, whereas a score of zero may steer the clinical discussion toward a less aggressive approach depending on other health factors. By contrast, routine testing for low-risk adults is less likely to yield actionable insights and may lead to unnecessary follow-up testing and radiation exposure.
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