Coronary Artery Calcium (CAC) scoring is a non-invasive medical imaging test used to detect and measure calcified plaque within the walls of the heart’s arteries. This procedure uses a specialized computed tomography (CT) scan to create detailed images of the coronary vessels. The primary purpose of CAC scoring is to provide a personalized assessment of an individual’s risk for future cardiovascular events, such as a heart attack. The presence of calcium is a direct sign of atherosclerosis, the underlying cause of most coronary artery disease. By quantifying this plaque burden, physicians gain insight into subclinical disease not apparent from traditional risk factors alone.
How Coronary Artery Calcium Scoring Works
The process of obtaining a CAC score begins with a non-contrast, low-dose computed tomography scan of the chest. This scan captures cross-sectional images of the heart without the need for an intravenous contrast dye. The CT scanner identifies dense calcium deposits because they appear bright white on the image.
These calcium deposits represent hardened atherosclerotic plaque accumulated within the coronary arteries. The final numerical result, known as the Agatston score, is derived from a calculation that considers both the area and the density of each calcified lesion detected. The area of the plaque is measured, and a weighted value is applied based on the maximum density of the calcium, often measured in Hounsfield Units.
The scores from all detected calcium specks in the four main coronary arteries are summed together to yield the total Agatston score. This method provides a standardized way to quantify the total volume of calcified plaque burden, serving as a direct marker of coronary atherosclerosis.
Interpreting the Agatston Score
The Agatston score serves as a tool for stratifying a person’s risk for coronary artery disease based on the amount of calcified plaque found. A score of zero is the best possible result, indicating no detectable calcified plaque and correlating with a very low risk of experiencing a heart attack in the near future. This finding often provides a “warranty period” of several years with a very low event rate.
Scores between 1 and 100 represent a mild amount of calcified plaque, suggesting a low to moderate risk of future cardiovascular events. A score in this range may prompt a physician to recommend more intensive lifestyle modifications or closer monitoring of other risk factors.
An Agatston score of 101 to 400 signifies a moderate amount of plaque and indicates a heightened risk that may necessitate the initiation of preventative medications. Scores exceeding 400 are considered extensive and are associated with a high volume of atherosclerotic plaque and a significantly elevated risk of a major cardiac event. Individuals in this highest category often warrant aggressive management and further diagnostic evaluation.
Evaluating the Predictive Accuracy
Coronary Artery Calcium scoring is considered highly accurate for predicting the presence or absence of subclinical coronary artery disease in asymptomatic individuals. The test’s accuracy is particularly notable for its strong negative predictive value, meaning a score of zero reliably indicates a very low likelihood of a near-term cardiac event. For patients with no calcification, the annual rate of major adverse cardiovascular events is extremely low, often less than one event per 1,000 patient-years.
The score significantly improves risk prediction when combined with traditional risk factors, such as cholesterol levels and blood pressure. Standard risk assessment tools, like the Framingham Risk Score, only account for clinical factors and may over- or underestimate a person’s true underlying disease burden. Adding the CAC score to these models results in a substantial reclassification of risk for many individuals.
Studies have shown that incorporating the Agatston score can correctly reclassify a significant percentage of patients into higher or lower risk categories than traditional scoring methods alone. This enhanced accuracy allows for more precise treatment decisions, particularly regarding the need for statin therapy. The presence of any calcium is a stronger predictor of future events than many individual traditional risk factors.
This test provides anatomical evidence of disease, which offers a prognostic advantage over risk scores based only on physiological and demographic data. For instance, a patient with a high cholesterol level but a CAC score of zero has a much lower long-term risk than a patient with a low cholesterol level but a high CAC score. The score is therefore a direct and independent predictor of cardiac death and myocardial infarction.
Limitations and Appropriate Patient Selection
Despite its strong predictive accuracy, CAC scoring has limitations that must be considered during interpretation and patient selection. The most significant limitation is that the scan only detects calcified, or hardened, plaque and cannot identify non-calcified, or “soft,” plaque. Soft plaque can still be unstable and lead to a sudden heart attack, meaning a low score does not completely rule out all forms of coronary disease.
Like all CT procedures, the scan involves a small amount of radiation exposure. Furthermore, the test is not universally covered by insurance, which can present a barrier to access for some patients. It is also not a functional test and cannot assess blood flow or the degree of existing arterial narrowing.
Current guidelines suggest that CAC scoring is most beneficial for asymptomatic adults who fall into the intermediate-risk category based on traditional assessment tools. For these individuals, the result—a score of zero or a high score—can definitively guide the decision to start or withhold preventative medications like statins. The test is generally not recommended for very low-risk patients, as the result is unlikely to change management, or for patients who are already at very high risk or have active symptoms, as aggressive treatment is already indicated.