The Coronary Artery Calcium (CAC) scan is a non-invasive imaging test that helps determine an individual’s risk of a heart attack or other adverse cardiovascular events. It uses a computed tomography (CT) machine to look for calcified plaque buildup in the coronary arteries, the vessels supplying blood to the heart muscle. This calcified plaque is a direct sign of atherosclerosis, or the “hardening of the arteries,” which develops over time. The result is the Agatston score, a powerful tool for risk stratification, especially in asymptomatic middle-aged or older people.
Understanding the Coronary Artery Calcium Score
The CAC scan is performed quickly using a specialized CT machine without intravenous contrast dye. The process quantifies the amount of calcium deposits found in the walls of the coronary arteries. The Agatston score is calculated by measuring the area of each calcified spot and multiplying it by a factor based on the calcium’s density.
The total score reflects the volume and density of the calcified plaque burden, which correlates strongly with the extent of atherosclerosis. The score only measures calcified, or hard, plaque, not the softer, non-calcified plaque that can also cause problems. Even so, the Agatston score is an independent predictor of future cardiac events and mortality.
Interpreting Scores by Absolute Risk Category
The absolute Agatston score is divided into four widely recognized categories, providing a general prediction of the 10-year risk for a cardiovascular event. A score of 0, often called the “power of zero,” suggests a very low risk of a heart attack over the next decade, with event rates typically below 2%. This score often leads to withholding statin therapy.
A score between 1 and 100 indicates mild or minimal plaque buildup and is associated with a low to mild risk. The 10-year event risk in this range is approximately double the risk associated with a score of zero. A score between 101 and 400 is considered a moderate burden of plaque, implying a moderate to high risk that often warrants the initiation of statin therapy.
A score above 400 represents a high or severe level of calcification, associated with a very high risk of a future cardiac event. Individuals with this score have a risk comparable to someone who has already had a heart attack. The risk for major cardiovascular events rises significantly across these categories, with event rates for scores over 300 ranging from 13.1% to 25.6% over a decade.
Contextualizing Scores for a 65-Year-Old
Interpreting a CAC score for a 65-year-old requires considering the patient’s age and gender alongside the absolute score. While 0 is the best result, some plaque accumulation is expected in people in their mid-sixties because atherosclerosis is a progressive process. The median CAC score for individuals aged 65 to 75 years is approximately 110 Agatston units.
A “good” score for a 65-year-old is one significantly lower than their peers, determined by the age- and sex-specific percentile. A score is considered favorable if it falls below the 50th percentile, meaning the person has less plaque than half of their demographic group. Conversely, a high-risk score for this age group is defined as one at or above the 75th percentile.
For a 65-year-old man, a score of 100 might be considered average or slightly below average. A score that places a 65-year-old at the 75th percentile or higher—for example, a score around 300 to 400—indicates an accelerated burden of atherosclerosis. This percentile-based context helps healthcare providers determine if the plaque burden is merely typical for age or if it represents an unusually high risk requiring more aggressive intervention.
Next Steps Following a CAC Result
The CAC score provides information that guides conversations between a patient and their physician about preventive care. For a score of 0, statin therapy is generally withheld, though lifestyle optimization and managing other risk factors remain important. If the score is between 1 and 99, the decision to start statin therapy is often individualized, especially if the patient is 55 or older or has other risk factors like diabetes.
A score of 100 or greater is a strong recommendation for initiating statin therapy, regardless of the patient’s cholesterol levels or traditional risk assessment. For very high scores, such as those above 300 or 400, high-intensity statin therapy is often recommended. Clinicians may also consider additional non-statin cholesterol-lowering medications to achieve lower LDL-C goals. Lifestyle modifications, including diet and exercise, are universally recommended to slow plaque progression, and aspirin therapy may be considered for scores over 100 where the benefit outweighs the bleeding risk.