A CAC test (coronary artery calcium test) is a quick, noninvasive CT scan of your heart that measures how much calcium has built up in the walls of your coronary arteries. That calcium is a direct marker of plaque buildup, and the amount detected translates into a numerical score that estimates your risk of a heart attack over the next several years. The scan takes only a few minutes, requires no injected dye, and delivers a radiation dose comparable to a mammogram.
How the Scan Works
You lie on a table that slides into a CT scanner, and the machine captures detailed images of your coronary arteries during a few heartbeats. Newer 256-slice scanners can image the entire heart in a single heartbeat, while older 64-slice machines need about five. No contrast dye is injected; the scanner is specifically looking for calcium deposits, which show up brightly on CT without any enhancement.
The radiation exposure is low, typically around 0.8 to 1.1 millisieverts depending on the scanner and your body size. For context, that’s roughly what you’d get from a mammogram and a fraction of what a full chest CT delivers. One occasional downside: the scan sometimes catches unrelated findings like small lung nodules, which can lead to follow-up tests and unnecessary worry even when they turn out to be harmless.
Understanding Your Score
The result is reported as an Agatston score, named after the cardiologist who developed the scoring method. It adds up the density and area of every calcified spot the scanner finds across all your coronary arteries. The categories break down like this:
- 0: No calcium detected. Very low risk. This is the best possible result and suggests a low chance of heart attack over the next decade.
- 1 to 99: Mild plaque. Mildly increased risk. Some buildup is present but limited.
- 100 to 299: Moderate plaque. Moderately increased risk of a heart attack or other cardiovascular event over the next three to five years.
- 300 or higher: Extensive plaque. Moderate to severely increased risk, signaling significant disease in the artery walls.
A zero score is powerful information. In one large study, a 70-year-old man with mild high blood pressure had an estimated 10-year heart disease risk of 9.3% based on traditional factors alone. After a CAC score of zero, that estimate dropped to 3.1%. The score essentially overrode a concerning-looking risk profile.
How the Score Affects Treatment Decisions
The CAC score is most useful for people in a gray zone of risk, where it’s genuinely unclear whether preventive medication is worthwhile. Current guidelines from the American College of Cardiology and American Heart Association recommend the test primarily for adults whose estimated 10-year cardiovascular risk falls between 5% and 20%, a range that covers a huge number of middle-aged adults.
If your score comes back at zero, current guidelines say it’s reasonable to hold off on starting a statin and recheck your calcium score in five to ten years. The exceptions are people with diabetes, a strong family history of early heart disease, or active smoking, where the risk stays elevated regardless of calcium levels.
A score between 1 and 100 makes a moderate-intensity statin reasonable, particularly if you’re 55 or older. Once the score crosses 100, or lands at or above the 75th percentile for your age, sex, and race, guidelines support statin therapy at any age. In practical terms, the test converts an abstract percentage into visible evidence of disease in your arteries, which often makes both doctors and patients more comfortable committing to long-term prevention.
What the Test Cannot Detect
A CAC scan only sees calcified, or “hard,” plaque. It does not detect soft plaque, the fatty, non-calcified deposits that can also narrow arteries and rupture to cause heart attacks. This means a score of zero does not guarantee perfectly clean arteries; it means there is no calcified buildup. For most people at low to intermediate risk, the absence of calcium is strongly reassuring. But in younger patients or those with aggressive risk factors, dangerous soft plaque can exist without any calcium present.
If your doctor needs to see the full picture, including soft plaque and the degree of artery narrowing, a CT coronary angiography is the next step up. That test uses injected contrast dye and delivers a higher radiation dose, but it visualizes both calcified and non-calcified plaque along with how much blood flow is being restricted.
Cost and Access
Most insurance plans, including Medicare, do not cover a CAC scan because it is considered a screening test rather than a diagnostic one. Out-of-pocket costs typically range from $100 to $400 at facilities that offer competitive pricing, though some imaging centers charge $400 to $800 at full price. A growing number of hospital systems have introduced low-cost or even free CAC screening programs to make the test more accessible. If you’re considering the scan, it’s worth calling a few local imaging centers to compare prices, as they vary widely even within the same city.
No special preparation is needed. You’ll be asked to avoid caffeine for a few hours beforehand and to wear comfortable clothing without metal snaps or zippers near your chest. The actual scan portion is over in under a minute on modern machines, though the full appointment with check-in and positioning typically takes 15 to 30 minutes. Results are usually available within a day or two.
Who Benefits Most From the Test
The CAC test adds the most value for adults between roughly 40 and 75 who have some cardiovascular risk factors (high blood pressure, elevated cholesterol, family history, or a history of smoking) but haven’t had a heart attack or been diagnosed with heart disease. It’s a tiebreaker: when standard risk calculators put you in an uncertain range, the calcium score pushes the decision clearly toward treatment or watchful waiting.
The test is less useful at the extremes. If you’re already high-risk and clearly need a statin, a CAC scan won’t change your management. If you’re young with no risk factors, the score will almost certainly be zero and won’t tell you anything new. The sweet spot is the large population of adults who fall somewhere in between, where a concrete number can replace years of ambiguity about whether prevention is truly needed.