A coronary calcium scan looks straight at your heart’s arteries and measures the calcified plaque that’s already there. For the right person, it settles a hard question: do you actually need to be on a statin, or can you safely wait? For the wrong person, it’s a dose of radiation and a little anxiety that changes nothing.
What is a CAC score, and what does the number mean?
A CAC scan is a quick CT that scores calcified plaque in your heart’s arteries, on a scale called the Agatston score. Zero means none detected. The number climbs with how much plaque you’ve built up. The rough bands the 2026 ACC/AHA guideline uses2: 0 is none, 1 to 99 mild, 100 to 299 moderate, 300 and up severe, 1,000 and up extensive. Risk follows the score closely. Compared with a zero, a score of 1 to 100 carries roughly 1.7 times the risk of a cardiovascular event, and 100 or more about 2.7 times, even after accounting for the usual risk factors (MESA cohort, a long-running study of about 6,800 adults).1 Above 300, your risk is in the range of someone who has already had heart disease.
One nuance worth knowing: the score is also read against your age and sex. Any calcium in your 40s is more concerning than the same score at 70, so a result at or above the 75th percentile for your age can matter even when the absolute number looks small.
Threshold table: what the CAC number usually changes
| CAC result | What it means | Usual decision impact |
|---|---|---|
| 0 | No calcified plaque detected | Often lets a borderline-risk person wait on a statin |
| 1 to 99 | Mild plaque | Age matters; in a younger adult it pushes more toward treatment |
| 100 to 299 | Moderate plaque | Strong reason to treat LDL and ApoB more aggressively |
| 300 or higher | Severe plaque | Risk approaches the range of known heart disease |
| 1,000 or higher | Extensive plaque | High-risk result that should not be treated as routine prevention |
The power of zero: when a scan lets you wait
The most useful result is often a zero. In MESA (about 6,800 adults followed for more than a decade; European Heart Journal, 2018)1, people with a CAC of zero had 10-year heart-disease risk around 1 to 5 percent, almost always under the 7.5 percent mark where we start seriously discussing a statin. So a zero can reasonably take a statin off the table for now, even if a risk calculator had been nudging you toward one. It isn’t permanent. A zero buys you roughly 3 to 7 years before it’s worth rescanning,3 sooner if you’re higher risk or diabetic.
Among people a risk score had already flagged for a statin, the estimated number you’d need to treat for 10 years to head off one cardiovascular event was about 64 if their calcium score was zero, versus about 28 if it was over 100.4 Same “eligible” patient, very different payoff.
Who should get one, and who shouldn’t?
CAC earns its keep for one job: the on-the-fence statin decision. The 2026 ACC/AHA guideline now gives it a strong recommendation2 for adults at borderline or intermediate risk when the choice isn’t clear, men from about 40 and women from about 45. Roughly 40 percent of intermediate-risk adults turn out to have a zero, which is reassuring and buys time; about 25 percent land at 100 or higher, which is a clear reason to treat.2
It’s not for everyone. If your risk is already low, the scan rarely changes anything and you’re paying for radiation you didn’t need. And if you already clearly need a statin, because of diabetes, an LDL over 190, or a strong family history, you don’t need a number to confirm it.
The practical details: it’s a roughly 10-minute non-contrast CT, no fasting, about 1 millisievert of radiation (close to a mammogram),2 and it usually runs $100 to $175 out of pocket, since insurance coverage is patchy.
Where CAC can mislead
The main limit: no randomized trial has shown that screening with CAC actually reduces heart attacks.6 What we have is strong evidence that it sorts people’s risk better than the standard calculators do,7 plus the modeled statin math above, not a trial proving the scan saves lives.
A zero is reassuring but not a force field. In one study, up to 14 percent of people with significant blockages had a calcium score of zero,5 because the scan only sees calcified plaque, not the softer kind that can still rupture. About one in ten scans also turns up an incidental finding, often a small lung nodule,2 that sends you for follow-up imaging you didn’t plan on.
And once you’re on a statin, repeat scans stop being useful, because statins actually raise the calcium number as they harden and stabilize plaque.2
When to get a CAC scan and when to skip it
If a risk calculator puts you in the borderline-to-intermediate zone and you and your doctor are honestly unsure about a statin, a CAC scan is one of the best tie-breakers we have. A zero means you can likely wait and recheck in a few years. A score over 100, or anything above the 75th percentile for your age,2 means it’s time to treat: get your LDL and ApoB down and keep your blood pressure, blood sugar, and smoking in line.
If you’re already clearly high-risk or clearly low-risk, skip the scan, because it won’t change the plan. The test is worth doing only when the result can actually change what you do next.