A CAC score, or coronary artery calcium score, is a number that reflects how much calcium has built up in the walls of your heart’s arteries. It’s measured with a quick, non-invasive CT scan of your chest, and the result tells you and your doctor how much hidden plaque is already forming in your coronary arteries, often years before any symptoms appear. A score of zero means no detectable calcium, while scores above 300 place you in a high-risk category for heart attack or stroke.
What the Scan Actually Measures
Calcium deposits form inside artery walls as part of atherosclerosis, the gradual buildup of fatty plaque that narrows and stiffens blood vessels. The amount of calcium in your coronary arteries is generally proportional to the total amount of plaque present. So while the scan is technically measuring calcium, it’s really giving you a snapshot of how much coronary artery disease has developed so far.
The scan itself takes seconds. You lie on a table while a CT scanner captures images of your heart, timed to your heartbeat so the pictures come out sharp. No contrast dye or needles are involved. The radiation exposure is low, with a median dose of about 2.3 millisieverts, roughly comparable to a mammogram. The entire appointment, including setup, typically takes about 10 to 15 minutes.
A computer then identifies every bright spot of calcium in your coronary arteries and assigns it a value based on its size and density. These individual values are added together into a single number called the Agatston score, named after the physician who developed the method. That total is your CAC score.
How to Read Your Score
CAC scores fall into several risk categories:
- 0: No detectable calcium. Very low risk. This is the best possible result and suggests minimal plaque burden.
- 1 to 99: Mildly increased risk. Some plaque is present, but the burden is relatively small.
- 100 to 299: Moderately increased risk. There’s a meaningful amount of plaque in the arteries.
- 300 and above: Moderate to severely increased risk. At this level, your risk of a heart attack or coronary death over the next decade may approach 28% if other risk factors are also present.
- Above 1,000: A distinct very high-risk group. People in this range have significantly greater risk of cardiovascular disease, cancer, and death from all causes compared to those with scores of 400 to 999.
Your score also gets compared to other people of the same age, sex, and ethnicity. A score in the 75th percentile or higher for your demographic group means you have more coronary calcium than most of your peers, which matters for treatment decisions even if your absolute number doesn’t look extreme.
Why It Outperforms Traditional Risk Factors
Standard heart disease risk calculators use your age, blood pressure, cholesterol levels, smoking status, and family history to estimate your chance of a cardiovascular event over the next 10 years. These calculators are useful, but they’re predictions based on population averages. A CAC score shows what’s actually happening in your specific arteries right now.
Since the 1990s, research has consistently shown that CAC scoring outperforms traditional risk factors in predicting heart attacks and strokes. Someone with textbook-perfect cholesterol numbers can still have a high CAC score, revealing hidden disease that blood tests alone would miss. Conversely, someone flagged as intermediate risk by a standard calculator might have a score of zero, suggesting they can safely hold off on aggressive treatment. A CAC score above 300 in a person without known heart disease carries a risk of major cardiac events equivalent to someone who already has established coronary artery disease.
Who Should Get the Test
Guidelines from the American College of Cardiology and American Heart Association recommend considering a CAC scan for adults aged 40 to 75 who fall into an intermediate risk zone (roughly a 7.5% to 20% estimated 10-year risk of a cardiovascular event) and whose cholesterol levels leave the treatment decision unclear. It’s also reasonable for selected people at borderline risk (5% to 7.5%) when the choice to start medication isn’t straightforward.
The scan is less useful at the extremes. If you’re already high risk due to diabetes, very high cholesterol, or known heart disease, you likely need treatment regardless of your calcium score. And if you’re young with no risk factors, the result will almost certainly be zero.
What a Score of Zero Does and Doesn’t Mean
A zero score is reassuring. It means no calcified plaque was detected, and your short-term risk of a cardiac event is very low. The result is durable enough that some guidelines consider a zero score valid for up to two years when making decisions about further testing.
But zero doesn’t mean zero risk. The scan detects only calcified plaque. Soft, non-calcified plaque, the kind that can rupture and trigger a heart attack, doesn’t show up. In a large international registry of over 10,000 symptomatic patients with zero calcium scores, about 13% had non-obstructive soft plaques and 3.5% had significant blockages above 50%. Among patients with chest pain and a zero score, roughly 1 to 2% turn out to have obstructive coronary artery disease on further imaging. That’s a small percentage, but it’s not nothing, especially if you’re having symptoms.
Still, the prognosis for those patients remains favorable. Studies tracking symptomatic patients with zero scores found that even the small number with underlying blockages did not have worse outcomes over two years of follow-up.
How Your Score Affects Treatment
The CAC score’s biggest practical impact is on the statin conversation. For people in that uncertain middle-risk zone, the score can tip the decision clearly in one direction.
A score of zero supports deferring statin therapy, since your actual disease burden is minimal despite what a risk calculator might predict. A score above 100, or one that places you above the 75th percentile for your age and sex, pushes toward starting or intensifying cholesterol-lowering treatment. At those levels, more aggressive management of LDL cholesterol is warranted, sometimes including additional medications beyond statins if a 50% reduction in LDL isn’t achieved with statins alone.
Beyond cholesterol, the score also informs decisions about blood pressure management and whether low-dose aspirin makes sense for prevention. It personalizes what would otherwise be a one-size-fits-all approach to heart disease prevention.
Cost and Insurance Coverage
Most insurance plans, including Medicare and Medicaid, do not cover CAC scans for people without symptoms. The test is considered a screening tool, and coverage for screening tests has historically lagged behind clinical use. Out-of-pocket costs range from about $50 to $400 depending on the facility and your location. Many imaging centers offer it at the lower end of that range as a self-pay option, making it one of the more affordable cardiac tests available.