New Northwestern Medicine Study Reveals Coronary Artery Calcium Scans Offer Limited Benefit for Most, But Prove Vital for Intermediate-Risk Patients

Coronary artery calcium (CAC) scans have experienced a surge in popularity over the past decade as a fast, relatively inexpensive computed tomography (CT) diagnostic tool designed to measure calcified plaque buildup within the arteries supplying blood to the heart. Touted by wellness advocates and preventive cardiologists alike, these scans are frequently marketed as a proactive way for individuals to look inside their bodies and assess their personal, long-term risk of heart disease. However, new research published in the Journal of the American Medical Association (JAMA) on August 26 indicates that the widespread, indiscriminate use of these scans may be largely unnecessary for the general population.

According to a comprehensive 10-year study led by researchers at Northwestern Medicine, adding a coronary artery calcium score to standard risk-prediction models provides only a marginal improvement for the population as a whole. Instead, the scan’s greatest clinical utility is restricted to a much narrower cohort of patients: specifically, those whose initial standard cardiovascular risk assessments place them in a borderline or intermediate risk category.

The findings arrive at a critical time in preventative medicine, as healthcare systems grapple with rising costs, patient anxieties, and the over-utilization of diagnostic imaging. By clarifying precisely who stands to benefit from a CAC scan, the Northwestern research team hopes to streamline clinical workflows, reduce unnecessary radiation exposure, and help physicians target preventative therapies more efficiently.

Understanding the Mechanics: PREVENT Versus Calcium Scans

To fully appreciate the implications of the new study, it is necessary to examine the two primary methodologies evaluated by the research team: the American Heart Association’s PREVENT risk calculator and the coronary artery calcium scan.

The primary cardiovascular risk calculator promoted by the American Heart Association (AHA) is known as PREVENT. This algorithmic tool estimates an individual’s statistical probability of developing cardiovascular disease over a 10-year or 30-year horizon. To generate this estimate, PREVENT relies on routinely collected clinical metrics, including systolic blood pressure, cholesterol panels, age, sex, kidney function, and whether the patient uses medications for hypertension or diabetes, or smokes tobacco. Because it requires only basic blood work and standard vital signs, PREVENT can be administered quickly in any routine outpatient physician’s office without incurring additional financial costs or subjecting the patient to radiation.

Conversely, a coronary artery calcium scan takes a distinctly physical, imaging-based approach. Utilizing a specialized CT scanner, the test captures cross-sectional images of the heart to detect deposits of calcium within the walls of the coronary arteries. The presence of calcified plaque correlates directly with the overall burden of coronary atherosclerosis. The resulting output—known as an Agatston score or simply a calcium score—provides a numerical representation of calcification. Generally, a score of zero indicates very low short-term risk, whereas higher scores (such as 100, 400, or higher) signify substantial plaque accumulation and a markedly elevated risk of experiencing a heart attack or stroke in the coming years.

For years, many clinicians operated under the assumption that combining these two distinct assessment methods—algorithmic risk calculation and physical plaque visualization—would yield a universally superior tool for predicting cardiovascular events. The Northwestern Medicine study put that hypothesis to a rigorous, long-term test.

Tracing the Research: A Decade-Long Investigation

To investigate the true incremental value of coronary artery calcium scans, senior study author Dr. Nilay Shah and his colleagues at the Northwestern University Feinberg School of Medicine turned to robust, established data. They examined longitudinal health records from more than 6,000 adult participants enrolled in the landmark Multi-Ethnic Study of Atherosclerosis (MESA).

The cohort comprised diverse men and women ranging in age from 45 to 79 years who were free of clinical cardiovascular disease at the study’s baseline. At the onset of the research period, each participant underwent both a coronary artery calcium scan and a comprehensive clinical evaluation, allowing researchers to calculate their baseline 10-year risk using the PREVENT framework. The research team then tracked the health trajectories of these individuals over a full decade, documenting real-world cardiovascular events—specifically non-fatal myocardial infarctions, strokes, and cardiovascular-related deaths.

During the 10-year follow-up window, approximately 6% of the study participants experienced a major adverse cardiovascular event. When the researchers analyzed the predictive power of the models, they discovered a surprising reality. When applied to the entire study population, adding the coronary artery calcium score to the PREVENT calculator produced only a negligible statistical improvement.

Statistically, the discrimination of the predictive model—measured by the C-statistic, which evaluates how accurately a model distinguishes between individuals who will experience an event and those who will not—rose only slightly from 0.73 using PREVENT alone to 0.75 when calcium scores were incorporated. For the broad population, the expensive imaging test added very little prognostic clarity beyond what a simple clinical calculator already provided.

The Pivotal Exception: Borderline and Intermediate Risk Patients

While the global population-level benefits were modest, a deeper subgroup analysis revealed a starkly different story for a specific segment of patients. When the researchers isolated data for individuals whose initial PREVENT scores placed them in the borderline or intermediate risk categories—defined as an estimated 3% to 9% chance of experiencing a cardiovascular event over the subsequent 10 years—the inclusion of a calcium scan proved clinically meaningful.

For patients trapped in this diagnostic gray area, the calcium score acted as a decisive tiebreaker. A score of zero among a borderline patient often reclassified their actual risk downward, suggesting they could safely defer aggressive preventative drug therapy. Conversely, a surprisingly high calcium score in an intermediate-risk patient provided definitive evidence that plaque was accumulating rapidly, signaling an urgent need for early intervention.

“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,” explained Dr. Shah, an assistant professor of medicine in the division of cardiology at Northwestern.

The Pitfalls of Indiscriminate Screening

The study’s authors caution that the rising popularity of coronary artery calcium scans has led to a culture of indiscriminate ordering, wherein patients outside the intermediate risk bracket undergo imaging without clear clinical justification. This practice carries notable downsides, both financial and physiological.

According to Dr. Shah, deploying calcium scans indiscriminately across low-risk populations yields virtually no actionable clinical benefit while exposing healthy individuals to unnecessary ionizing radiation and out-of-pocket medical costs. Routine screening in low-risk cohorts frequently generates false positives or incidental findings that trigger a cascade of secondary diagnostic tests, inducing profound patient anxiety without altering long-term outcomes.

At the opposite end of the spectrum, ordering calcium scans for patients who are already classified as high-risk is similarly redundant. Current clinical guidelines dictate that individuals at high risk for cardiovascular disease should be prescribed statin therapy and lifestyle modifications regardless of what a imaging scan reveals. If a patient’s clinical profile already mandates treatment, a calcium scan serves no purpose in guiding management, effectively wasting healthcare resources.

“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,” Dr. Shah emphasized. “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.”

Clinical Implications and the Power of PREVENT

Cardiovascular disease remains the leading cause of mortality in the United States, accounting for roughly one in every five deaths and affecting approximately 10% of American adults aged 30 to 79. Despite these sobering statistics, a significant proportion of heart attacks and strokes are preventable through early risk identification and the judicious use of preventative therapies, most notably statins—medications designed to lower low-density lipoprotein (LDL) cholesterol and stabilize arterial plaque.

The Northwestern study highlights the exceptional baseline utility of the American Heart Association’s PREVENT equations. Even when evaluated entirely on its own, without any advanced imaging input, PREVENT demonstrated a high degree of accuracy in forecasting future cardiovascular events. This validation is a significant win for primary care physicians, who can rely on standard office-based metrics to stratify patient risk efficiently and cost-effectively.

By demonstrating that advanced imaging should be reserved for a strategically targeted subset of patients, the study provides a roadmap for more rational resource allocation within cardiology and primary care. Physicians are now better equipped to use diagnostic tools hierarchically: starting with a robust clinical calculator like PREVENT, and reserving the CT scanner for those ambiguous cases where uncertainty remains high.

Future Directions and Unanswered Questions

While the study offers profound insights into cardiovascular risk assessment, the research team acknowledges certain limitations that point toward necessary avenues for future scientific inquiry.

The current cohort, derived from the MESA study, primarily evaluated adults aged 45 to 79. Consequently, additional research is required to determine how well these findings translate to younger adults who may be entering early stages of subclinical atherosclerosis. Furthermore, Dr. Shah noted that certain demographic and ethnic groups—such as South Asian and Filipino populations, which often experience unique cardiovascular risk profiles—require targeted investigation to evaluate whether calcium scores provide different prognostic thresholds in these specific populations.

The study, titled "Predictive Utility of Coronary Artery Calcium Added to the PREVENT Atherosclerotic Cardiovascular Disease Equations," was published in JAMA with financial support from the American Heart Association (grant 24CDA1266732) and the National Heart, Lung, and Blood Institute. Alongside Dr. Shah, the Northwestern research team included co-authors Xiaoning Huang, Lucia Petito, Norrina Allen, Dr. Philip Greenland, and Dr. Sadiya Khan.

As healthcare systems continue to balance technological innovation with economic prudence, this latest evidence from Northwestern Medicine establishes a clear standard: when it comes to assessing heart disease risk, more testing is not always better. By focusing advanced imaging precisely where it matters most—the borderline and intermediate risk patients—clinicians can optimize outcomes while protecting patients from the pitfalls of unnecessary medicalization.