Coronary Artery Calcium (CAC) score
Research Summary
A Coronary Artery Calcium (CAC) score is a specialized, non-invasive imaging test that uses a non-contrast computed tomography (CT) scan to measure the amount of calcified plaque in the heart's arteries. Unlike a standard CT, this scan is specifically 'gated' to the heart's rhythm to ensure clear images of the coronary vessels. It is a powerful tool for identifying subclinical atherosclerosis—heart disease that has begun to develop but hasn't yet caused symptoms like chest pain or a heart attack. The test results are typically expressed as an Agatston score, which provides a quantitative estimate of a person's total burden of coronary artery disease.
The scan works by detecting calcium deposits, which are dense and appear as bright white spots on CT images because they block X-rays more than soft tissue. Since calcium is not normally found in the coronary arteries except as a component of atherosclerotic plaque, its presence is a highly specific marker for disease.
- Detection: The scanner identifies areas with a density of 130 Hounsfield Units (HU) or higher.
- Scoring (Agatston Method): For each calcified area, the software multiplies the area of the plaque (in mm²) by a 'density factor' (ranging from 1 to 4).
- Total Score: The scores for all individual plaques are summed to create the total CAC score.
- Percentiles: Results are often compared to others of the same age, sex, and ethnicity (using databases like the MESA study) to determine a percentile rank, which can be even more predictive than the raw score alone.
Key Benefits
The CAC score is one of the best predictors of future cardiac events, outperforming traditional risk calculators that only look at age, blood pressure, and cholesterol. It offers a personalized assessment of actual disease rather than just statistical probability. Because it is non-invasive and takes only 10–15 minutes with no contrast dye required, it is a low-burden way to gain significant clarity on heart health. Additionally, seeing actual plaque in their own arteries has been shown to improve patient adherence to lifestyle changes and medication.
Considerations
The primary downside is exposure to a small amount of ionizing radiation (roughly equivalent to a mammogram), which makes it unsuitable for frequent repetition. It also cannot detect 'soft' (non-calcified) plaque, which can still rupture and cause a heart attack—this is particularly relevant in younger patients or smokers whose plaque may not have calcified yet. Finally, the test can lead to incidental findings (e.g., nodules in the lungs) that may require follow-up scans and cause unnecessary anxiety, and it is often not covered by insurance, requiring an out-of-pocket cost.
Current ACC/AHA (2024/2025) and ESC guidelines recommend the CAC score primarily as a 'risk adjudicator' for asymptomatic adults to guide the use of preventative therapies like statins and aspirin.
- Who should get it: Asymptomatic adults aged 40–75 years with an intermediate 10-year cardiovascular risk (typically 7.5% to 20%). It is also recommended for those with a 'borderline' risk (5% to 7.5%) if risk-enhancing factors like a strong family history are present.
- Interpreting Results:
- Score = 0: Indicates a very low risk of events over the next 10 years (the 'power of zero'). It may allow for the safe deferral of statin therapy, unless the patient is a heavy smoker, has diabetes, or a very strong family history of premature heart disease.
- Score = 1–99: Indicates mild plaque. Statin therapy is generally favored, especially for those over age 55.
- Score = 100–399: Indicates moderate disease and a high risk of events. Preventive medication (statins and potentially aspirin) is strongly recommended.
- Score ≥ 400: Indicates extensive plaque. Intensive preventive measures and further clinical evaluation are required.
- When to avoid: It is generally not recommended for individuals already at 'very high risk' (who should be on statins regardless) or those with known coronary disease (prior stents or bypass), as the score will not change the management plan.
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