The Coronary Artery Calcium (CAC) scan is a non-invasive computed tomography (CT) test that measures calcified plaque in the heart’s arteries. This measurement, called the Agatston score, quantifies the extent of atherosclerosis, a condition where plaque builds up and narrows the arteries. The CAC score is a powerful predictor of future cardiovascular events, such as heart attack or stroke, helping to refine an individual’s risk assessment.
Eligibility for Initial Testing
The CAC test is not a universal screening tool but is used to clarify risk in specific groups of asymptomatic adults. It is recommended for men and women aged 40 to 75 who fall into the borderline or intermediate categories of estimated 10-year risk for atherosclerotic cardiovascular disease (ASCVD). This typically means a risk calculation between 5% and 20% based on traditional factors like cholesterol and blood pressure. The test helps decide if preventive medications, such as statins, would offer a significant benefit.
Patients considered low-risk (10-year ASCVD risk below 5%) generally do not require the test, as calcification is unlikely. Conversely, those already classified as high-risk, such as people with pre-existing heart disease, bypass surgery, or a stent, also typically do not need the scan. In these high-risk cases, the disease is confirmed, and treatment is maximized, meaning the test would not change the treatment plan.
The CAC scan is especially useful for individuals with a borderline 10-year risk (5% to less than 7.5%) who have additional risk-enhancing factors. These factors include a strong family history of premature heart disease, high lipoprotein(a) levels, or certain inflammatory conditions. For these patients, the test can reclassify them into a higher-risk category, justifying the initiation of preventive therapy.
Interpreting Your First Calcium Score
The Agatston score factors in both the area and density of calcium deposits, ranging from zero to over 1,000. This number strongly indicates the total plaque burden and associated risk. A score of zero is highly favorable, indicating no detectable calcified plaque and a very low risk of a cardiovascular event over the next five to ten years.
Scores from 1 to 100 suggest a mild plaque burden and modestly elevated risk compared to a score of zero. This result often prompts an intensified focus on lifestyle modifications and may lead to low- to moderate-intensity statin therapy if other risk factors are present. A score between 101 and 400 represents a moderate amount of calcified plaque, placing the individual in a moderate to high-risk category.
A score in the 101–400 range typically warrants a more aggressive preventive strategy, often including high-intensity statin medication. Scores exceeding 400 indicate an extensive plaque burden and are associated with a very high risk of a future event. For these patients, the risk is comparable to those who have already experienced a heart attack, necessitating the most intensive medical management.
Guidelines for Repeat Testing Frequency
The decision to repeat a CAC test is driven by the initial score and subsequent risk management. If the initial score is zero, a repeat scan is generally not recommended for at least five to ten years. A zero score offers a strong “warranty period” against short-term cardiovascular events, and retesting sooner provides little additional information.
If the initial score was low to moderate (between 1 and 400), retesting is usually deferred for three to five years, or often longer. Plaque progression is a slow process, so a short interval between scans offers little predictive value. The goal of retesting in this group is to monitor disease progression, especially if the initial result did not lead to the initiation of statin therapy.
If a patient with a moderate score (101–400) has already started aggressive risk-reducing therapy, retesting is often unnecessary within the first few years. For individuals with a very high initial score (typically over 400), a repeat test is rarely indicated. These patients are already classified as high-risk and placed on maximum preventive therapy, meaning a new score would not change the treatment plan.
When Risk Changes Override the Timeline
While general guidelines suggest multi-year intervals for repeat testing, changes in a patient’s health profile can justify an earlier reassessment. The development of a new, significant cardiovascular risk factor, such as new-onset diabetes or severe hypertension, may override the standard timeline. In these scenarios, the accelerated disease process means an earlier repeat scan could inform a necessary intensification of therapy.
Similarly, if a patient with a low or moderate score develops new cardiac symptoms, such as chest discomfort or shortness of breath, a repeat scan might be considered as part of a broader diagnostic workup. The emergence of symptoms suggests a possible progression of atherosclerosis that warrants immediate investigation, potentially sooner than the standard interval.
Some physicians may consider a repeat scan after several years of intensive statin therapy to assess treatment effectiveness, though this remains debated. Ultimately, the decision to repeat the test outside of standard intervals must be made in consultation with a cardiologist. This decision weighs the minimal radiation exposure against the potential for a change in treatment strategy.