Coronary calcium score: what it measures, what it means and what guidelines say

A coronary calcium scan is a quick CT scan that looks for hardened plaque in the arteries that feed the heart. The result is a single number, the calcium score. The 2026 US cholesterol guideline suggests it selectively, for people whose estimated heart risk sits in the middle, where the choice about a cholesterol-lowering statin is a close call.

A new 10-year study in JAMA (the Journal of the American Medical Association) found the score added little for people whose risk was clearly low or clearly high. This guide explains what the score measures, what the numbers mean, what the guideline says and what the new study found.

What a coronary calcium scan shows

Coronary artery disease develops slowly over time when plaque builds up inside your coronary arteries. Plaque is a mix of fat, cholesterol, calcium and other substances, and over the years some of it hardens.

The scan uses CT (computed tomography), a type of x-ray imaging, to find that calcium. RadiologyInfo, run by two radiology societies, describes it as a noninvasive way of obtaining information about the presence, location and extent of calcified plaque in the heart’s arteries. The exam takes less than 20 minutes, and people can go straight back to their normal day.

What it does not show matters just as much. A calcium score describes plaque that has hardened, or calcified. It cannot see softer plaque, and it does not show whether an artery is narrowed. It estimates future risk in people without symptoms; it is not a test for blockages, and chest pain and other heart symptoms are investigated with different tests.

What your calcium score means

RadiologyInfo grades the extent of coronary artery disease according to your calcium score:

Calcium score	What it suggests
0	No calcified plaque seen
1 to 10	Minimal plaque
11 to 100	Mild plaque
101 to 400	Moderate plaque
Over 400	Extensive plaque

The number is not a diagnosis on its own. Your calcium score is one part of your overall risk picture, alongside age, blood pressure, cholesterol, diabetes and smoking.

What it can do is split people who look alike on paper. In the JAMA study, among those at borderline risk, the share who had a heart attack, stroke or related event over 10 years was:

• 1.9% with a score of 0
• 3.9% with a score of 1 to 99
• 7.4% with a score of 100 to 299
• 14.3% with a score of 300 or more

That is more than a sevenfold spread between people whose standard risk estimate was the same.

Who the 2026 guideline suggests a calcium scan for

The starting point is your estimated 10-year risk of a heart attack or stroke. In the US this is now calculated with the American Heart Association’s PREVENT (Predicting Risk of cardiovascular disease EVENTs) equations. They were built for US adults 30 to 79 years of age without known heart disease, and use traditional risk factors (smoking status, systolic blood pressure, cholesterol, blood pressure or statin medicines and diabetes) plus a measure of kidney function.

A new US cholesterol guideline from the American College of Cardiology, the American Heart Association and other groups retires and replaces the 2018 guideline. It sorts that risk into four bands: low (under 3%), borderline (3% to under 5%), intermediate (5% to under 10%) and high (10% or more). It newly recommends selective use of coronary artery calcium scoring for people in the middle two bands.

That matters because the guideline also widens who is offered a statin. One analysis estimated that 87.5 million US adults are now statin eligible, including 21.5 million who were newly statin eligible. The newly eligible were largely younger and lower risk, with an average 10-year risk of 3.1%, which falls in the borderline band where the guideline suggests considering a scan.

What the 10-year calcium score study found

The JAMA study drew on the Multi-Ethnic Study of Atherosclerosis, which enrolled adults aged 45 to 79 at six US sites and scanned their hearts at the start. A total of 6098 participants were included, and about half had some calcium. Over 10 years, 366 people, or 6%, had a heart attack, stroke or related event.

The researchers compared how well PREVENT predicted those events with and without the calcium score. Overall, the gain was small. On a standard scale where 0.5 is a coin toss and 1 is perfect, accuracy rose from 0.73 to about 0.75. The authors conclude that adding the score across all risk groups overall only modestly improved predictions.

The middle groups were different. There, the score moved people up or down a risk band in a way that matched what later happened to them, which the authors say supports scanning selectively, in those with borderline to intermediate risk.

What does a calcium score of zero mean?

A score of zero is the lowest-risk result. RadiologyInfo notes that a score of zero may support delaying or holding off on cholesterol-lowering medicine in some people.

It does not last forever. One analysis followed 3,116 participants from the same study who started with a score of zero and had follow-up scans over 10 years. By 10 years, 53% had developed some calcium. The researchers estimated that a zero score stays reliable for roughly 3 to 7 years depending on sex and race/ethnicity, and the presence of diabetes was associated with a shorter safe interval.

Zero also does not mean no plaque at all. Heart disease, especially in people below 50 years of age, can be present without calcium, as softer plaque the scan cannot see.

What are the downsides of a calcium scan?

Like any CT scan, it uses x-rays, and RadiologyInfo notes that the radiation dose for this procedure varies. A high calcium score may sometimes be followed by other diagnostic tests, which do not always help and can have side effects of their own.

Cost is the other catch. Not all health insurance plans cover the scan, and costs vary by region.

How a calcium score fits into treatment decisions

A score does not decide treatment on its own. RadiologyInfo summarizes current national guidelines this way: finding any coronary calcium generally supports treating cholesterol to a lower target, and the target is lower still when more calcium is present.

The new study adds a caveat about where the scan earns its place. The score changed risk estimates most for people in the borderline and intermediate bands, and added little outside them. Whether a score changes any one person’s treatment depends on the rest of their risk picture, including blood pressure, diabetes, smoking and family history, which is assessed by their doctor.

What calcium scan research cannot tell us yet

The JAMA study measures prediction, not benefit. It does not show that people who have a scan, and act on the result, have fewer heart attacks than people who do not; that would need a randomized trial.

Participants were scanned years ago and treated by the standards of the time. The cohort was ethnically mixed but may not match everyone, and the zero-score estimates come from the same group of volunteers.