Who really needs a heart calcium scan?

But new research from Northwestern Medicine suggests the scan may provide its greatest benefit to a narrower group of patients than previously assumed.

Researchers followed more than 6,000 adults for 10 years and found that, for the overall study population, adding a coronary artery calcium score provided only a small improvement over PREVENT, the American Heart Association's primary cardiovascular risk calculator.

How Heart Calcium Scans Measure Risk

PREVENT estimates a person's chance of developing cardiovascular disease over the next 10 or 30 years using commonly available health information (such as blood pressure, cholesterol, age, and sex).

A coronary artery calcium scan takes a different approach. The CT scan looks for calcium-containing plaque inside the coronary arteries. The resulting calcium score reflects the amount of detectable calcified plaque. In general, a higher score is associated with a greater risk of future cardiovascular disease.

The new findings suggest that calcium scores become particularly useful when PREVENT initially places someone in a borderline or intermediate risk category. Among these patients, the additional scan provided a clearer indication of who was more likely to develop cardiovascular disease and who was less likely.

"Coronary artery calcium scans are becoming more widely available and less expensive," said study senior author Dr. Nilay Shah, assistant professor of medicine in the division of cardiology at Northwestern University Feinberg School of Medicine. "Our findings suggest that not everyone necessarily needs or would benefit from a coronary artery calcium scan for the purpose of predicting risk of heart attack and stroke."

Shah said the findings also highlight potential downsides of using the scans when they are unlikely to change a patient's treatment.

"Routinely using a calcium scan in people who are at low risk may result in unnecessary radiation exposure, testing and costs with unclear clinical benefits," Shah added. "Using calcium scans in people who are at high risk is likely to result in unnecessary testing because these individuals are recommended to start a statin regardless of what the calcium scan shows."

The study was published on Aug. 26 in JAMA.

Comparing Predictions With Real Outcomes

To investigate how much additional information calcium scans provide, Shah and his colleagues examined data from more than 6,000 adults ages 45 to 79 who participated in the Multi-Ethnic Study of Atherosclerosis.

At the beginning of the study, each participant received both a coronary artery calcium score and a PREVENT estimate of their likelihood of experiencing a cardiovascular event within the following 10 years.

Researchers then tracked what actually happened.

Over the next decade, 6% of the participants experienced either a heart attack or stroke. When the team compared predictions that included calcium scores with those based on PREVENT alone, the overall improvement was modest.

The model's discrimination, which measures how effectively it distinguishes between people who will and will not experience a cardiovascular event, increased only slightly. It rose from 0.73 using PREVENT to 0.75 when calcium scores were included.

The picture changed, however, when researchers focused specifically on people whose initial PREVENT scores placed them in the borderline or intermediate risk categories (those initially deemed to have a 3% to 9% risk of heart disease within 10 years).

For this group, including the calcium score produced a more meaningful improvement in predicting future cardiovascular events.

"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," Shah explained.

Finding the Patients Most Likely to Benefit

About 10% of U.S. adults age 30-79 have cardiovascular disease, which remains the nation's leading cause of death. Yet many heart attacks, strokes and other cardiovascular events can be prevented, Shah said.

Accurately identifying a person's risk can help doctors determine who is most likely to benefit from preventive treatments, including statins, which lower cholesterol and reduce cardiovascular risk.

"The findings help us understand how best to use the available tools to estimate someone's risk of a heart attack or stroke. That provides more precise guidance for who is most likely to benefit from using a statin to help prevent heart disease," Shah said.

Shah added that the results also support the clinical usefulness of the relatively new PREVENT calculator. Even without calcium scan results, PREVENT performed well at predicting cardiovascular risk.

Questions That Still Need Answers

The researchers said additional studies are needed to determine how much calcium scores improve PREVENT estimates in certain populations.

That includes higher risk groups such as South Asian and Filipino adults, Shah noted. More research is also needed in younger people because participants in this study were between ages 45 and 79 when the research began.

Other Northwestern co-authors are Xiaoning Huang, Lucia Petito, Norrina Allen, Dr. Philip Greenland and Dr. Sadiya Khan.

The study is titled, "Predictive Utility of Coronary Artery Calcium Added to the PREVENT Atherosclerotic Cardiovascular Disease Equations." It was supported by the American Heart Association (grant 24CDA1266732) and the National Heart, Lung, and Blood Institute (contracts 75N92020D00001, HHSN268201500003I, N01-HC-95159, 75N92020D00005, N01-HC-95160, 75N92020D00002, N01-HC-95161, 75N92020D00003, N01-HC-95162, 75N92020D00006, N01-HC-95163, 75N92020D00004, N01-HC-95164, 75N92020D00007, N01-HC-95165, N01-HC-95166, N01-HC-95167, N01-HC-95168, N01-HC-95169 and grant K23HL157766).