A coronary artery calcium (CAC) scan is a quick, low-radiation CT scan that looks for calcified plaque in the arteries of the heart. It has become one of the most useful tools for deciding who needs treatment to prevent heart attacks, especially when the decision about starting a statin is not clear-cut. Here is what the test measures and how to understand your result.
What the scan measures
Over time, cholesterol-rich plaque can build up inside the coronary arteries. Some of that plaque becomes calcified. A CAC scan detects this calcium and produces a score, often called the Agatston score. Calcium in the coronary arteries is a direct sign of atherosclerosis, and the amount is closely linked to the risk of heart attack and other cardiovascular events over the following years.
The scan does not require dye or an IV. You lie on a CT table for a few minutes while the scanner takes images timed to your heartbeat. The radiation dose is low.
Who may benefit from a CAC scan
A CAC scan is most useful for adults without known heart disease whose 10-year risk of a heart attack or stroke is in a borderline or intermediate range, typically people aged 40 to 75, when it is not clear whether to start statin therapy. It can also help people who:
- Have a family history of early heart disease
- Prefer not to take a statin unless clearly needed
- Have risk factors that standard calculators may not fully capture
It is generally not needed for:
- People already diagnosed with heart disease, who should already be on preventive treatment
- People at very low risk, where the result is unlikely to change anything
- People at clearly high risk, who should usually be treated anyway
Understanding your score
| CAC score | What it suggests | Typical next steps |
|---|---|---|
| 0 | No detectable calcified plaque; short-term risk is low | In many people at borderline or intermediate risk, statins can often be deferred unless other strong risk factors exist; recheck in several years |
| 1–99 | Mild plaque | Statin therapy is generally favored, especially from age 55 |
| 100–399 | Moderate plaque | Statin therapy recommended, along with lifestyle changes |
| 400 or more | Extensive plaque | Higher-intensity prevention; your doctor may consider additional testing if you have symptoms |
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Reports often also give a percentile, comparing your score with people of the same age, sex and ethnicity. A score at or above the 75th percentile suggests higher-than-average risk for your age.
Why a score of zero matters
A score of 0 is reassuring. It means there is no calcified plaque, and the short-term risk of a heart attack is low. Many guidelines support delaying statin therapy in people with a zero score unless they smoke, have diabetes, a strong family history of early heart disease, or very high cholesterol. A zero score does not rule out soft (non-calcified) plaque, so it does not mean heart disease can never develop. A repeat scan after several years may be considered.
What a high score means
A higher score means more plaque and a higher risk of future events. It does not necessarily mean an artery is blocked, and a high score alone is not a reason for a stent or bypass surgery if you have no symptoms. It is a strong signal to:
- Start or intensify statin therapy
- Control blood pressure and blood sugar
- Stop smoking
- Exercise regularly and eat a heart-healthy diet
- Discuss aspirin with your doctor, as it may be considered for some people with high scores and low bleeding risk
If you have symptoms such as chest pain or breathlessness with exertion, a CAC score is not the right test on its own. Your doctor may order a stress test or CT coronary angiography instead.
Can statins make the score go up?
Sometimes. Statins stabilize plaque and can make it more calcified, which may slightly increase the score while actually lowering risk. That is why repeat scans are not usually recommended just to monitor the effect of treatment.
Cost and insurance
CAC scans are relatively inexpensive compared with many imaging tests, and many hospitals and imaging centers offer them at a fixed self-pay price. Insurance coverage varies, and many plans do not cover them for screening. Ask about the price before booking.
The bottom line
A CAC scan gives a direct look at whether plaque is building in your heart arteries. A score of 0 is reassuring and can help some people avoid or delay medication, while higher scores point to more aggressive prevention. It is most valuable when you and your doctor are unsure whether to start a statin.
This article is for general information and does not replace medical advice.