A CT calcium score is a number that reflects how much calcium-containing plaque has built up in the arteries supplying your heart. The scan itself takes just a few minutes, uses a low dose of radiation, and produces a single number called the Agatston score. That score helps estimate your risk of having a heart attack or stroke in the coming years, especially when standard risk factors like cholesterol and blood pressure leave the picture unclear.
How the Scan Works
Calcium deposits form inside arterial plaque as part of the gradual process of atherosclerosis, where fats, cholesterol, and other substances collect along artery walls. A coronary calcium scan uses a CT scanner to take rapid X-ray images of your heart, timed to your heartbeat so the pictures are sharp. The software then measures every visible speck of calcium in your coronary arteries, factoring in both the total area and the density of each deposit. Those measurements get combined into a single number: the Agatston score.
The radiation exposure is remarkably low. Modern scanners deliver roughly 0.8 to 1.1 millisieverts, which is comparable to the dose from a mammogram or a lung cancer screening CT. There’s no contrast dye involved, no needles, and no recovery time. You lie still on a table for about 10 minutes, and results are typically available the same day or within a few days.
What the Numbers Mean
Your Agatston score falls into one of several risk tiers:
- 0: No detectable calcium. This is considered very low risk. In one large study, patients with a score of zero had only a 0.5% rate of major cardiac events (heart attack, stroke, or cardiac death) over 3.5 years.
- 1 to 99: Mild plaque buildup and mildly increased risk. Even a small amount of calcium signals that atherosclerosis has started.
- 100 to 299: Moderate plaque buildup. Risk of a cardiac event rises meaningfully in this range.
- 300 and above: Moderate to severe buildup. Patients with scores of 400 or higher had a 6.8% rate of major cardiac events over 3.5 years in the same study, more than 13 times the rate seen with a zero score.
Some people score above 1,000, which represents extensive calcification. Many of them have no symptoms at the time of scanning, which is part of why the test exists: it catches disease that hasn’t announced itself yet.
For all-cause mortality, even a small amount of calcium matters. A study published in JACC: Cardiovascular Imaging found that people with scores of just 1 to 10 had roughly double the risk of dying from any cause compared to those with a score of zero, after adjusting for traditional risk factors like age, blood pressure, and cholesterol.
Who Should Get One
This test isn’t designed as a screening tool for everyone. The 2019 guidelines from the American College of Cardiology and American Heart Association recommend it as a decision-making aid for people whose heart disease risk is genuinely uncertain. In practice, that means two groups: people at borderline risk (a 10-year cardiovascular risk of 5% to 7.5%) and people at intermediate risk (7.5% to 20%). For someone in those ranges, a calcium score can tip the scales, either reassuring you that aggressive treatment isn’t needed or revealing hidden plaque that justifies starting a statin or intensifying lifestyle changes.
If your risk is already clearly high, perhaps because of established diabetes, very high cholesterol, or a prior heart event, the scan adds little. You’d already qualify for treatment. And if your risk is very low based on age, blood pressure, and other factors, the scan is unlikely to change anything either.
What a Zero Score Does and Doesn’t Tell You
A score of zero is genuinely reassuring. It’s associated with a very low rate of heart attacks and cardiac death over the following 5 to 10 years. But it doesn’t mean your arteries are perfectly clean. Plaque in its earlier stages is soft, made up mostly of fats and inflammatory cells without significant calcium. These non-calcified plaques don’t show up on a calcium scan.
Research has consistently shown that unstable plaques, the kind most likely to rupture and trigger a heart attack, actually contain less calcium than stable plaques. The calcium score works not because it identifies the single dangerous plaque, but because it reflects the overall burden of disease in your arteries. Someone with extensive calcification almost certainly has non-calcified plaque too, raising their total risk. A score of zero makes that total burden very unlikely but not impossible, particularly in younger people or those with strong risk factors like smoking or diabetes. In the mortality study mentioned above, smoking and diabetes were the two factors most associated with cardiac events even among people who scored zero.
Cost and Insurance
A coronary calcium scan typically costs between $100 and $400 out of pocket. Insurance coverage varies and the test isn’t always reimbursed, so it’s worth checking with your plan ahead of time. Many imaging centers and hospitals offer it as a self-pay option at the lower end of that range, making it one of the more affordable cardiac tests available. Given that it requires no dye, no fasting, and minimal radiation, the barrier to getting one is mostly about knowing whether it’s appropriate for your risk level.
What Happens After the Scan
Your score doesn’t exist in isolation. It gets interpreted alongside your age, sex, blood pressure, cholesterol, smoking status, and family history. A score of 150 in a 45-year-old carries different implications than the same score in a 70-year-old, because calcium accumulates with age and a high score at a younger age suggests faster-than-expected disease progression.
If your score is zero, you and your doctor may decide that lifestyle measures alone are sufficient for now. If your score is elevated, especially above 100, the conversation typically shifts toward cholesterol-lowering medication, tighter blood pressure management, and more structured follow-up. Some clinicians also use the score to motivate patients directly. Seeing a concrete number tied to plaque in your own arteries can make abstract risk feel real in a way that cholesterol numbers sometimes don’t.
Repeat scans are sometimes done years later to track whether calcium is progressing, though guidelines don’t specify a fixed interval. The score only goes up over time; calcium deposits don’t shrink. What treatment aims to do is slow the rate of new plaque formation and stabilize existing plaque so it’s less likely to cause problems.