Zero radiation is not the goal, but a 10-minute scan that quietly counts calcium deposits along the walls of your heart’s arteries can deliver an Agatston score from zero to over 1,000 that estimates your 10-year risk of a heart attack. The scan detects only calcified plaque, the hardened buildup that X-rays can pick up, and it does not see soft, non-calcified plaque that has not yet mineralized.
Because calcium is a fingerprint of atherosclerosis, the disease behind most heart attacks, the score often catches risk that cholesterol blood tests miss entirely.
This guide explains what the scan does, how scoring works, and what to do with your number. You’ll learn how to read your results, when the test makes sense for you, and how it compares with stress tests and angiograms.
What a CAC Test Measures Inside Your Arteries
Coronary artery calcium forms when cholesterol-rich plaque in your artery wall hardens over years, the way old pipes collect mineral scale. A CT scanner detects that calcium because it is dense enough to block X-rays, even in amounts too small to spot on a standard X-ray. The scanner ignores soft, vulnerable plaque that has not yet calcified, so a zero score means “no visible calcium right now,” not a guaranteed clean bill of health for you.
The score itself comes from a method developed by Dr. Arthur Agatston in the early 1990s and now bears his name. It multiplies the area of each calcium deposit by a density weighting and sums them into one number. A zero, a 47, and an 800 carry radically different risk profiles, and the categories below are how cardiologists typically frame them.
How the Agatston Score Is Calculated
Each pixel of bright white on your scan that exceeds a set density threshold (130 Hounsfield units) gets flagged as calcium. The software tallies every flagged region across all slices of your heart, weighs the densest ones more heavily, and rolls them into one final number. That single number drives every downstream decision for you, from whether you start a statin to how often you get rechecked.
| Agatston Score | What It Means | Rough Heart Attack Risk |
|---|---|---|
| 0 | No detectable calcium | Very low (under 1% per year for most adults) |
| 1–99 | Mild plaque present | Low to moderate |
| 100–299 | Moderate plaque burden | Moderate to high |
| 300–399 | Extensive plaque | High |
| 400 and above | Severe plaque | Very high; risk comparable to someone who already survived a heart attack |
Framingham Risk Score calculators rely on age, blood pressure, and cholesterol to estimate 10-year risk, and they routinely miss plaque in people whose cholesterol looks fine. The Multi-Ethnic Study of Atherosclerosis (MESA), a long-running NIH-sponsored study, showed that adding CAC scoring to standard risk models dramatically improves who actually needs treatment.
That predictive lift only matters if the scan itself is something patients can realistically complete.
How the Scan Works and What You Experience
Your whole appointment takes about ten minutes once you’re on the table. No fasting, no IV, no exercise stress, and no recovery time. You lie still on your back while the scanner circles your chest a few times, holding your breath for roughly ten seconds per pass so the images stay sharp.
Radiation, Contrast, and What to Wear
Expect a radiation exposure near 1 mSv, comparable to a mammogram and far below a standard chest CT (which can run 5–7 mSv). The scan uses no dye and no needles, so allergic reactions to contrast aren’t a concern. Wear something loose with no metal across your chest, and skip the morning coffee only if your clinic specifically asks.
Most people walk out before your phone finishes loading the parking meter.
Who Reads Your Scan
A radiologist or cardiologist certified in cardiac CT reviews every image. Your report should include the Agatston score, the volume score, and sometimes a vessel-specific breakdown (left anterior descending, circumflex, right coronary). Many centers now post your results within 24 hours through a patient portal.
Once those numbers land in your portal, the next challenge is making sense of what each one actually signals.
Reading the Score: What Zero, Low, Moderate, and High Really Mean
A score of zero is good news in the short term but isn’t a free pass forever. A 45-year-old with zero calcium today can develop meaningful plaque a decade later, especially with a family history of early heart disease. Most guidelines suggest rechecking every five years when your score is zero, sooner if your risk factors shift.
Low Scores (1–99): Early Warning, Not an Emergency
A score in this range means the disease has started in your arteries but is still in the early innings. Think of it like finding early rust on a car: fixable with maintenance, not a reason to panic.
A 52-year-old man with a score of 35, normal blood pressure, and LDL around 130 mg/dL might delay a statin if his 10-year ASCVD risk stays below 7.5%, while someone with diabetes and the same score usually starts one.
Moderate to High Scores (100–299 and 300+): Time to Act
Once your score crosses 100, plaque burden is significant enough that most cardiologists recommend a statin regardless of your cholesterol numbers. At 300 and above, your risk of a major cardiac event climbs steeply, comparable to a survivor of a prior heart attack. Scores in this range often trigger a stress test or a coronary CT angiogram to look for blockages that might need more than medication.
Higher scores demand follow-up imaging, but deciding who should get scanned in the first place is a separate question.
Who Benefits Most From Getting a CAC Scan
The test is not for everyone. It’s most useful for adults whose risk sits in a gray zone, where the decision to start medication isn’t clear from bloodwork alone.
- Borderline or intermediate risk: Adults 40–70 with a 10-year ASCVD risk between 5% and 20% get the clearest answer from a CAC score. A zero can prevent unneeded medication; a high score can justify starting one.
- Strong family history: When a first-degree relative had a heart attack before age 55 (men) or 65 (women), calcium scoring reveals whether inherited risk has already left a mark.
- Diabetes before age 50: Diabetes masks traditional risk markers, and a CAC score gives an actual picture of your arteries rather than an estimate.
- Statin users tracking progress: A repeat scan every 3–5 years can show whether plaque growth is slowing under treatment, useful when you want objective feedback.
The American Heart Association and American College of Cardiology both endorse CAC scoring as a “risk enhancer” when the decision to treat isn’t clear. Skip the scan if you’re already high risk (over 20% 10-year risk) or already known to have coronary artery disease, because the result won’t change your management.
Where CAC Fits Among Stress Tests, Angiograms, and Risk Calculators
A CAC scan finds silent plaque in your arteries before symptoms ever appear. Stress tests and angiograms work the opposite way, looking for blockages that already limit blood flow or cause chest pain. Knowing which tool does what saves you from the wrong test at the wrong time.
| Test | What It Detects | When It’s Used | Radiation / Invasiveness |
|---|---|---|---|
| CAC scan | Calcified plaque burden (Agatston score) | Asymptomatic, borderline-risk adults | ~1 mSv, no dye, no needles |
| Stress test (ECG or echo) | Blood flow problems under exertion | Chest pain, shortness of breath, or abnormal ECG | None to minimal |
| Coronary CT angiography | Soft and hard plaque, narrowing of arteries | Symptoms present, or high CAC score needing closer look | ~3–5 mSv, IV contrast |
| Invasive coronary angiogram | Blockages visible on X-ray with contrast | Suspected acute coronary syndrome or planned intervention | Catheter through the wrist or groin |
Pairing Your Score With Risk Calculators
Dropping your calcium score into an ASCVD or PREVENT calculator (tools like MDCalc host both) sharpens the decision on statins and aspirin far better than cholesterol alone. A 48-year-old woman with LDL 140, normal blood pressure, and a CAC score of 0 might dodge a statin entirely, while the same woman with a score of 220 would likely start one despite her “average” cholesterol.
After the Results: Concrete Steps for Each Score Band
Numbers mean nothing without a plan. Here’s what cardiology guidelines generally recommend once your score lands.
- Score of 0: Recheck in 5 years. Stay the course with diet, exercise, blood pressure, and glucose control. No statin needed in most cases.
- Score 1–99: Review your full lipid panel and blood pressure. A shared decision on statin therapy with your clinician makes sense, especially with diabetes, family history, or LDL above 160.
- Score 100–299: Statin initiation is the default, along with tighter blood pressure control. A stress test referral sometimes follows if you have symptoms.
- Score 300+: Aggressive lipid and blood pressure management, often a statin plus a second medication. Some clinicians add a coronary CT angiogram to rule out soft plaque or significant narrowing.
Bring your score to your next appointment and ask, “Does this change my plan?” That’s the question that turns your number into action.
Insurance and Cost Reality
Most major insurers cover CAC scoring when ordered for an appropriate indication, though coverage varies. Without coverage, your out-of-pocket cost typically runs $75 to $300, depending on region and facility. Call the imaging center, give them the CPT code (often 75571 or 71271), and ask what your plan actually pays before scheduling.
What the Scan Cannot Tell You
CAC scoring misses soft, non-calcified plaque in your arteries, the unstable kind that can rupture and cause a sudden heart attack. A zero score doesn’t guarantee your safety, particularly if you’re a younger adult, a smoker, or someone with a strong family history. The scan also can’t tell whether a specific calcium deposit is restricting blood flow; that’s a job for stress testing or angiography.
Bottom Line
One number can replace years of guesswork, because the Agatston score turns silent plaque buildup into a single, actionable figure that no other routine screening delivers as cheaply or as fast. If you’re 40 to 70 with borderline cardiovascular risk, this single scan can clarify whether medication is worth starting, deferring, or skipping altogether. Talk it over with your clinician, share your score, and let that number guide a plan tailored to your arteries rather than guesswork.
FAQ
What is a CAC test used for?
That measures calcium in your coronary arteries to predict your 10-year risk of a heart attack, especially when cholesterol and blood pressure alone don’t give a clear answer. The result helps you and your clinician decide whether to start a statin, escalate treatment, or hold off.
Is a CAC test worth it?
Borderline or intermediate cardiovascular risk in adults aged 40 to 70 is exactly where this scan earns its keep, often sparing years of unneeded medication or justifying a timely start to therapy. Outside that window, the result rarely changes your management.
What is a normal CAC score?
Zero means zero, and that single digit carries more reassurance than almost any other reading your doctor can hand you after a heart scan. Any score above zero indicates some plaque buildup, with your risk rising as the number climbs through 100, 300, and beyond.
How accurate is a coronary calcium scan?
Coronary calcium scans are highly reproducible, with the same person’s score typically varying by less than 10% between scans done on the same scanner. Accuracy depends on scanner quality and the technologist’s protocol, but modern cardiac CT is considered very reliable for what it measures.
Does insurance cover a CAC scan?
Borderline cardiovascular risk is the indication most carriers recognize, though coverage for the scan still varies widely depending on which insurer is writing the check. Your out-of-pocket cost without coverage typically falls between $75 and $300 depending on the facility.
Can a CAC score be zero?
Younger adults, women, and people without traditional risk factors frequently land on the chart at zero, and that clean reading can genuinely happen. A zero score means no visible calcium at the time of your scan, not a guarantee against future plaque buildup.
