Coronary Artery Calcium Score: When the Scan Helps a Decision

Your heart risk score came back "intermediate", and you are not sure about starting a statin. Or a friend had a "heart scan" and you wonder if you need one. A coronary artery calcium scan can help in some cases, but not in all. This guide explains when the scan is useful and how clinicians read the result.

What the scan is

A coronary artery calcium (CAC) scan is a CT scan of the heart. It looks for calcium in the walls of the coronary arteries, the arteries that feed the heart muscle. Calcium is a sign of older, hardened plaque.

• It takes a few minutes.
• No needles or dye are used.
• It uses a low dose of radiation.

The result is called an Agatston score. A score of 0 means no calcium was seen. Higher scores mean more calcified plaque.

What the score tells you

Calcium shows that plaque is present. More calcium means more plaque and higher risk. The Multi-Ethnic Study of Atherosclerosis (MESA) followed more than 6,000 adults for about 10 years [4]. Heart attack and stroke rates rose steadily as calcium scores rose. People with a score of 0 had low event rates over 10 years [4].

Common score groups are:

• 0: no calcified plaque seen
• 1 to 99: mild
• 100 to 399: moderate
• 400 or higher: severe

Reports may also give a percentile. This compares your score with people of the same age, sex, and background.

What your doctor looks at

When the scan helps

The scan is most useful when the decision about a statin is truly unclear [1] [2]. This is usually when:

• Your 10-year risk is borderline or intermediate.
• You have no known heart disease.
• You are not already clearly high risk, such as with very high LDL or diabetes with other risk factors.
• You and your clinician would act differently based on the result.

US guidance

The 2026 ACC/AHA dyslipidemia guideline gives CAC a clearer role when the decision to start or step up cholesterol treatment remains uncertain [1]:

• A score of 0 may support putting off a statin for a while in selected people without major high-risk conditions.
• Any calcium increasingly favours treatment as the score rises.
• A score of 1,000 or higher marks very high risk. The guideline supports lowering LDL by at least half and to below 55 mg/dL in that case.

The US Preventive Services Task Force (USPSTF) takes a more cautious view. In 2018 it said the evidence was not enough to judge the benefits and harms of adding CAC to standard risk scores in people without symptoms [3]. The USPSTF lists an update on CAC as in progress [3].

Canadian guidance

The 2021 Canadian Cardiovascular Society (CCS) guideline says CAC may be considered for adults 40 and older at intermediate risk when the treatment choice is uncertain [2]. A score of 100 or more, or at or above the 75th percentile, supports starting a statin. A score of 0 suggests a statin may be held off for now, except in people with strong risk factors such as smoking, diabetes, or a strong family history of early heart disease [2].

When the scan does not help

• If you have chest pain or other symptoms. You need a different kind of test.
• If you already have heart disease, a stent, or a past heart attack.
• If you are already clearly at high risk and treatment is recommended anyway.
• If you already take a statin. Statins can make plaque more calcified, so scores may rise even when treatment works.

Downsides to consider

• Radiation, though the dose is low.
• Incidental findings: the scan can show spots in the lungs or other organs. Most are harmless but may lead to more scans [1].
• Cost: the scan is often not covered by public plans or insurance. Check before you book.
• A score of 0 does not rule out soft plaque that has not yet calcified, especially in younger adults and smokers.

Experts also note that CAC treatment thresholds are based mainly on observational studies, not trials that compared scan-guided care with usual care [1].

What happens during the scan

• You lie on your back on a table that moves through the CT scanner.
• Small sticky pads on your chest track your heartbeat, so pictures are taken between beats.
• You hold your breath for a few seconds at a time.
• The whole visit is often under 30 minutes, and you can go back to your normal day right after.

A radiologist or cardiologist reads the scan, and the report goes to the clinician who ordered it.

Questions to ask your clinician

• Would a calcium scan change my treatment plan?
• What is my 10-year risk without the scan?
• If my score is 0, what would we do? If it is above 100?
• Is the scan covered for me, and what does it cost?
• What happens if the scan finds something outside the heart?
• Do I have risk factors that matter even with a score of 0?
• Would a repeat scan ever be useful for me?

When to get care quickly

A calcium scan is not a test for symptoms. Call 911 for chest pain or pressure, shortness of breath, cold sweat, sudden weakness, or trouble speaking. Do not book a scan instead of getting urgent care.

Bottom line

A coronary calcium scan shows how much calcified plaque is in your heart arteries. It helps most when your risk is in the middle and the statin decision is unclear. A score of 0 may support waiting in some people, while higher scores favour treatment. Canadian and US cardiology guidance support selective use, while the USPSTF says the evidence for routine use is not yet enough.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.