A coronary artery calcium (CAC) score is a number that reflects how much calcified plaque has built up in the arteries supplying your heart, and it falls into a straightforward risk ladder: zero means very low risk, 1 to 99 means mildly increased risk, 100 to 299 means moderately increased risk, and 300 or above means moderate to severely increased risk. But the raw number alone does not tell the full story. How old you are, your sex, and how your score compares to people like you all shape what a given number actually means for your health and what your doctor might recommend doing about it.
The Agatston Score and What Each Range Means
When you get a calcium score, the number you receive is almost always an Agatston score, named after the physician who developed the method in 1990. The scan picks up bright spots of calcium in the coronary arteries and calculates a total based on the density and area of each deposit. The result is a single number that gets slotted into one of several risk categories.1PubMed Central. An Update on Coronary Artery Calcium Interpretation at Chest and Cardiac CT
- Score of 0: Very low risk. No detectable calcified plaque in the coronary arteries.
- Score of 1–99: Mildly increased risk. Some plaque is present, but the burden is relatively small.
- Score of 100–299: Moderately increased risk. A meaningful amount of calcified plaque has accumulated.
- Score of 300 or higher: Moderate to severely increased risk. Substantial plaque burden, and in many cases scores climb into the thousands.
These cutoffs have been used for decades and are supported by large studies linking higher scores to a greater likelihood of heart attacks and other cardiovascular events over the following years. That said, the original scoring system was acknowledged from the start to be somewhat arbitrary in how it weighs plaque density and area.2Elsevier / ScienceDirect (JACC: Cardiovascular Imaging). Coronary Artery Calcium Scoring: Is It Time for a Change in Methodology? The categories have held up remarkably well in predicting outcomes, but there is nothing magical about the thresholds at 100 or 300. They are useful clinical breakpoints, not precise biological boundaries. A score of 98 and a score of 102 carry similar implications, even though they fall in different categories.
Why a Zero Score Carries So Much Weight
Of all the possible results, a score of zero gets the most attention from cardiologists, and for good reason. In a large multiethnic study, a CAC score of zero turned out to be the single strongest negative risk marker available, outperforming other measures like carotid artery thickness.3Circulation. Role of Coronary Artery Calcium Score of Zero and Other Negative Risk Markers for Cardiovascular Disease: The Multi-Ethnic Study of Atherosclerosis (MESA) In practical terms, this means a zero score substantially lowers the estimated probability that you will have a coronary event in the near future, even if other risk factors like cholesterol or family history suggest you might be at higher risk.
This is the situation where a calcium score changes clinical decisions most clearly. If a traditional risk calculator puts you in a borderline or intermediate risk zone and your doctor is on the fence about whether to start you on a statin, a zero score can tip the conversation toward holding off on medication. You still have risk factors, and you still need to manage them, but the absence of visible calcium provides strong reassurance that aggressive drug therapy may not be necessary right now.
A zero score is not a guarantee, though. Younger people and people with very aggressive disease can have dangerous soft (non-calcified) plaque that the CT scan simply does not detect. Calcium scoring measures calcified deposits specifically, and the scan is blind to other forms of plaque. A zero is tremendously reassuring, but it is not a clean bill of health if other clinical signs point in a different direction.
When Your Score Seems Misleading
A common frustration is getting a number and not knowing what it means for someone of your age and sex. A 70-year-old man with a score of 150 is in a very different situation from a 45-year-old woman with the same number. The raw Agatston score does not adjust for demographics, and this is where age and sex percentiles come in.
The Multi-Ethnic Study of Atherosclerosis, known as MESA, generated detailed tables showing the distribution of calcium scores across thousands of adults of different ages, sexes, and racial and ethnic backgrounds who were free of clinical heart disease. These distributions let you compare your score against what is typical for people like you.4Lippincott Williams & Wilkins. Distribution of coronary artery calcium by race, gender, and age: results from the Multi-Ethnic Study of Atherosclerosis (MESA) Someone in the 75th percentile or higher for their age and sex has more calcium than most of their peers, which carries additional risk information beyond the raw number alone. Someone at the 25th percentile, even with a nonzero score, is tracking with the lower end of what is expected for their demographic.
This percentile context matters because calcium accumulates naturally as you age. Older adults often have some coronary calcium without it signaling imminent danger, while a modest score in a younger person can indicate that atherosclerosis is progressing unusually fast. Many imaging centers now include age and sex percentiles on the report alongside the Agatston number, but not all do. If yours does not, the MESA calculator is freely available online.
How the Score Changes Treatment Decisions
Calcium scoring is not meant for everyone. Current guidelines give it a favorable recommendation specifically for adults whose estimated 10-year risk of a cardiovascular event falls in the borderline range (roughly 5 to under 7.5 percent) or the intermediate range (about 7.5 to under 20 percent), particularly when the decision about whether to start statin therapy is genuinely uncertain.5PubMed Central. Coronary Artery Calcium Scoring in Asymptomatic Patients In other words, the scan is most useful when your risk profile is ambiguous enough that a tiebreaker could shift what your doctor recommends.
For people already at very high risk, say those with established heart disease, diabetes, or extremely elevated cholesterol, the scan rarely adds new information. Treatment is already warranted. And for people at very low risk, a zero score would merely confirm what was already expected, making the scan and its radiation exposure unnecessary for most of them.
The practical power of the score lies in reclassification. Among borderline-risk adults, a meaningful percentage turn out to have scores above 100 when they actually get scanned. One recent study found that roughly a fifth of patients classified as borderline risk by traditional calculators had a calcium score above 100, bumping them into the intermediate risk category where statin therapy is more strongly considered.6Elsevier. Coronary artery calcium burden across the pooled cohort equation versus the American Heart Association PREVENT risk calculator The flip side is equally important: many people in that borderline zone have scores of zero, which allows them to defer medication with reasonable confidence.
This reclassification is not limited to one particular risk calculator. The same study examined a newer risk calculator called PREVENT and found that an even larger share of borderline-risk patients in that model, about 35 percent, had calcium scores above 100.6Elsevier. Coronary artery calcium burden across the pooled cohort equation versus the American Heart Association PREVENT risk calculator The takeaway is consistent: risk calculators based on traditional factors alone misclassify a substantial number of people, and calcium scoring corrects the picture in both directions.
What the Score Cannot Tell You
People sometimes treat a calcium score like a comprehensive report card on their arteries, and that overreads what the test does. A few important limitations are worth understanding.
First, the score measures only calcified plaque. Atherosclerosis involves multiple types of plaque, including soft, lipid-rich deposits that have not yet calcified. These soft plaques are actually the ones more likely to rupture and cause a sudden heart attack. A person with little calcium but a significant burden of soft plaque will score low on the CT but may still be at real risk. This is why a low score in someone with strong clinical risk factors should not end the conversation.
Second, the score tells you about plaque quantity, not about whether any particular artery is significantly narrowed. You could have a high score with calcium spread evenly across your arteries, none of them severely blocked, or a moderate score with most of the calcium concentrated in a single vessel that is near-critically narrowed. The scan typically is not performed with contrast, so it cannot evaluate how much blood flow is actually getting through. If symptoms like chest pain or shortness of breath are present, the appropriate next step is usually a different kind of test, such as a stress test or a CT angiogram with contrast, rather than just a calcium score.
Third, the score is a snapshot. It does not tell you how fast plaque is accumulating. Two people with the same score may be on very different trajectories depending on their risk factors and treatment.
Should You Get Repeat Scans
This is one of the less settled areas in calcium scoring. Because calcium in the arteries does not go away once it is there (statins slow new plaque formation and may stabilize existing plaque, but they do not dissolve calcium), your score will either stay the same or go up over time. It will not go down. That raises the question of whether a repeat scan years later adds useful information, and the answer depends on the situation.
If your initial score was zero, guidelines generally do not recommend re-scanning for at least several years. A zero score has been shown to carry a durable low-risk signal for roughly five to ten years in most people, though this is less certain for those with strong family histories or rapidly changing risk factors like new-onset diabetes. Scanning again at year two or three after a zero result rarely changes management.
If your initial score was nonzero, the question of repeat scanning is more nuanced. Some cardiologists use follow-up scans to see how fast the score is rising, reasoning that rapid progression is a marker of more aggressive disease. A score that jumps from 50 to 200 over a few years might prompt more aggressive treatment. But the evidence supporting routine serial scanning for all patients is not as robust as the evidence supporting the initial scan, and the added radiation, though modest, does add up. Most guideline bodies have not endorsed a standard re-scanning interval for everyone.
Radiation, Cost, and Access
A coronary calcium scan delivers a low dose of radiation, roughly comparable to one or two mammograms. This is far less than a diagnostic cardiac CT angiogram or a nuclear stress test, which is one reason calcium scoring has become popular as a screening tool. The scan itself takes only a few minutes and does not require contrast dye or any special preparation beyond briefly holding your breath.
The scan is widely available at imaging centers and hospitals in most of the United States, and the out-of-pocket cost for an uninsured or cash-pay patient typically runs somewhere between $75 and $300 depending on the facility. Insurance coverage has historically been inconsistent. Medicare and many private insurers have not routinely covered calcium scoring as a screening test, even though clinical guidelines endorse it for the appropriate risk groups. This is slowly changing, with some insurers beginning to cover the scan when it is ordered for patients in the borderline or intermediate risk categories. If your doctor recommends one, it is worth checking with your insurer beforehand, but even out of pocket the cost is modest relative to most cardiac imaging.
How Ethnicity Factors Into the Results
Calcium distribution in the coronary arteries varies across racial and ethnic groups in ways that researchers are still working to fully understand. The MESA data showed that, at the same age and sex, white and Hispanic adults tended to have higher calcium scores on average than Black and Chinese American adults.4Lippincott Williams & Wilkins. Distribution of coronary artery calcium by race, gender, and age: results from the Multi-Ethnic Study of Atherosclerosis (MESA) This does not mean Black adults are at lower cardiovascular risk overall; heart disease outcomes in Black Americans are among the worst of any group, driven by factors like hypertension, access to care, and systemic health disparities. What it does mean is that a given calcium score may carry somewhat different implications depending on your background, and that race-specific percentile tables exist precisely for this reason.
The practical point is that a score of 120 in a 55-year-old Black woman sits at a different percentile than a score of 120 in a 55-year-old white man, and both of those carry different weight than the same score in a 55-year-old Hispanic man. Any cardiologist familiar with the data will account for this context, but if your imaging report only gives a raw Agatston number and a generic risk category, you might be missing part of the picture. The MESA online calculator lets you plug in your age, sex, race, and score to see exactly where you fall relative to a comparable population free of known heart disease.
Calcium Scores Found Incidentally on Other Scans
An increasing number of people learn about coronary calcium not because they went looking for it, but because it showed up on a CT scan performed for another reason entirely, most commonly a lung cancer screening CT or a chest CT done after a trauma or for persistent cough. These scans cover the same anatomy and often pick up calcium in the coronary arteries as an incidental finding.
The challenge with incidental findings is that the scan may not have been performed using the precise technical settings used for formal Agatston scoring, meaning the number reported may be an estimate rather than a precise Agatston value. That said, researchers have increasingly argued that even rough calcium assessments from non-gated chest CTs provide clinically useful information.1PubMed Central. An Update on Coronary Artery Calcium Interpretation at Chest and Cardiac CT A radiologist noting moderate or severe coronary calcification on your lung screening CT is telling you something real, even if the number lacks the precision of a dedicated calcium score study. If coronary calcium shows up unexpectedly on any chest CT, it is worth raising the finding with your primary care doctor or cardiologist to determine whether it changes your overall risk management.
Some health systems have begun automatically flagging incidental coronary calcium and routing it into cardiovascular risk workflows, a recognition that millions of people getting lung CTs every year are, in effect, also getting a peek at their coronary artery health. Whether this practice becomes standard depends on how consistently it improves outcomes, but the trend is toward making use of information that is already being captured rather than ignoring it.