The Agatston score is a number that represents how much calcium has built up in your coronary arteries. It comes from a special CT scan of your heart, and it’s used to estimate your risk of a heart attack or other cardiovascular events. A score of zero means no detectable calcium and very low risk, while scores above 300 or 400 signal significantly elevated risk.
How the Score Is Calculated
During a coronary calcium scan, a CT machine takes rapid X-ray images of your heart. Software then identifies bright spots of calcium in the walls of your coronary arteries. For each calcium deposit, two things are measured: the physical area of the deposit and how dense (bright) it appears on the scan.
Density is measured in Hounsfield units, a standard scale for CT imaging. Each deposit gets a density weighting factor from 1 to 4, with denser calcium scoring higher. A deposit measuring 130 to 199 Hounsfield units gets a factor of 1, 200 to 299 gets a 2, 300 to 399 gets a 3, and anything 400 or above gets a 4. The area of each deposit is multiplied by its density factor, and then every deposit across all your coronary arteries is added together. That total is your Agatston score.
What the Score Ranges Mean
Scores are grouped into risk categories:
- 0: No detectable calcium. Very low risk. This is sometimes called the “power of zero” because event rates in people with this score fall below the threshold where preventive medications typically show benefit.
- 1 to 99: Mildly increased risk. Some plaque is present, but the overall burden is low.
- 100 to 299: Moderately increased risk. Studies show people in this range have roughly 2.5 times the risk of death or heart attack compared to those with scores below 100, with an 8-year survival rate around 90%.
- 300 and above (especially 400+): Moderate to severely increased risk. People with scores at or above 400 face about 4.5 times the risk of death compared to low scorers. Their 8-year survival rate drops to around 82%, and their combined rate of death or heart attack runs about 3% per year.
Raw Score vs. Percentile
A raw Agatston score of 150 means something very different for a 75-year-old man than for a 50-year-old woman. Calcium naturally accumulates with age, and the rate differs by sex and ethnicity. To account for this, your score can be converted into a percentile that compares you to people of the same age, sex, and racial or ethnic group.
The MESA (Multi-Ethnic Study of Atherosclerosis) calculator, freely available online, is the standard tool for this conversion. It covers adults aged 45 to 84 who identify as White, African American, Hispanic, or Chinese. If your raw score puts you above the 75th percentile for your demographic group, that carries more clinical weight than the raw number alone, because it means you have more calcium than most people like you.
Who Should Get a Calcium Scan
Current guidelines from both U.S. and European cardiology societies recommend calcium scoring selectively, not as a routine screening for everyone. The primary use is for people at borderline or intermediate cardiovascular risk, typically estimated at a 5% to 20% chance of a heart event over the next 10 years based on standard risk calculators that factor in age, cholesterol, blood pressure, and smoking status.
For these “in between” patients, the score helps resolve uncertainty. A zero score can justify holding off on a statin. A high score can tip the decision toward starting one. For people already at clearly high risk (established heart disease, very high cholesterol, diabetes), the scan usually won’t change management. And for people at very low risk, it’s generally unnecessary.
What the Scan Is Like
The scan itself is quick and noninvasive. You lie on a table that slides into a CT scanner, and the images are captured in a matter of seconds, synchronized to your heartbeat using electrodes on your chest. No contrast dye is injected, and no preparation is needed beyond possibly avoiding caffeine beforehand.
Radiation exposure is relatively low. The median effective dose is about 2.3 millisieverts, roughly comparable to a mammogram or a few months of natural background radiation. That said, doses vary widely by facility and protocol, ranging from under 1 to over 10 millisieverts, so the equipment and technique matter.
What Happens After a Positive Score
If your score comes back above zero, the response depends on how high it is and what your other risk factors look like. For most people with a positive score, the core recommendations are cholesterol-lowering medication (typically a statin, sometimes combined with other drugs), a diet lower in saturated fat, regular exercise, and aggressive management of blood pressure, blood sugar, and smoking if any of those are problems. For scores above 400, clinicians generally aim for more intensive cholesterol lowering, targeting very low LDL levels. These are considered lifelong strategies, not short-term fixes, because the calcium reflects years of plaque accumulation.
A positive score does not mean you need a stent or surgery. It means you have atherosclerosis, and the goal shifts to slowing or stopping its progression before it causes symptoms.
What the Score Cannot Tell You
The biggest limitation of the Agatston score is that it only detects calcified plaque. Coronary arteries can also contain “soft” plaque, made of cholesterol and inflammatory cells, that hasn’t yet hardened with calcium. This soft plaque doesn’t show up on a calcium scan but can still narrow arteries and, in some cases, rupture to cause a heart attack.
This creates what cardiologists call the “zero calcium paradox.” A score of zero is genuinely reassuring for asymptomatic people, with very low event rates over the following 5 to 10 years. But for someone already experiencing chest pain or other symptoms, a zero score does not rule out significant blockages. Published case reports document severe coronary narrowing from noncalcified plaque in patients with zero calcium. The reassuring “power of zero” applies mainly to asymptomatic screening, not to evaluating active symptoms.
The score also tells you nothing about which specific arteries are affected or how much blood flow is actually restricted. Two people with the same total score can have very different distributions of plaque. And because the score reflects calcium density and area, a single dense deposit and many scattered smaller ones can produce similar numbers despite representing different patterns of disease.