Topic Reviews A-Z
Coronary Artery Calcium (CAC) Score Topic Review
The coronary artery calcium score enhances clinical risk stratification for patients at risk for atherosclerotic coronary disease.
Generating a coronary artery calcium (CAC) score requires a quick CT scan, with no intravenous (IV) access or IV contrast required. Results are available within minutes. The CT scan reliably detects arterial calcification, and the amount of calcium present correlates with the risk for significant angiographic stenosis. Coronary calcium scoring is available for a cash fee at many centers without a physician's order or an appointment.
The Agatston algorithm — a semi-automated tool developed by Arthur Agatston, MD, in 1990 to quantify arterial calcium — is used to compute a numerical score. A score of 0 indicates no detectable coronary calcification. In contrast, a score above 400 suggests a 90% chance of an angiographically significant stenosis.
According to the 2018 Multi-Society and American College of Cardiology/American Heart Association Guideline on the Management of Blood Cholesterol and the 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease, atherosclerotic cardiovascular disease (ASCVD) risk assessment should be considered in all patients, with a focus on patients between 40 and 75 years of age. [Grundy SM, et al. J Am Coll Cardiol. 2018; 3a; Arnett DK, et al. J Am Coll Cardiol. 2019;3a] Primary prevention patients in this age group who have low-density lipoprotein cholesterol (LDL-C) between ≥ 70 mg/dL and < 190 mg/dL and who do not have diabetes may be classified into four risk groups, based on their 10-year estimate of ASCVD risk. These include the low-risk (< 5%), borderline-risk (5% to < 7.5%), intermediate-risk (≥ 7.5% to < 20%) and high-risk (≥ 20%) groups.
The decision whether to initiate statin therapy depends on the assigned risk group. In the low-risk and high-risk group, the recommendations are clear — no statin therapy and high-intensity statin therapy, respectively, are indicated. In the borderline- and intermediate-risk groups, the decision to initiate statin therapy depends on the overall risk estimate and the presence of risk enhancers, such as family history of ASCVD.
If the decision to initiate statins in patients with intermediate and select patients with borderline risk remains uncertain, the ACC/AHA guidelines state that it is reasonable (Class of Recommendation IIa) to use a CAC score in the decision to withhold, postpone or initiate statin therapy: [Grundy SM, et al. J Am Coll Cardiol. 2018; 3b,4a; Arnett DK, et al. J Am Coll Cardiol. 2019;20a]
- If the CAC score is 0, it is reasonable to withhold statin therapy and reassess in 5 to 10 years, as long as higher-risk conditions are absent (diabetes, family history of premature coronary artery disease, cigarette smoking).
- If the CAC score is 1-99, it is reasonable to initiate statin therapy for patients 55 years of age and older.
- If the CAC score is ≥ 100 and/or ≥ 75th percentile, it is reasonable to initiate statin therapy.
Patients that might benefit from knowing their CAC score is 0 include [Grundy SM, et al. J Am Coll Cardiol. 2018;25a]:
- those reluctant to initiate statin therapy who wish to better understand their risk and potential for benefit;
- those concerned about the need to reinstitute statin therapy after discontinuation for statin-associated symptoms;
- older individuals (55-80 years for men; 60-80 years for women) with a low risk factor burden who are unsure whether they would benefit from statin therapy; and
- middle-aged adults (40-55 years) with borderline (5% to < 7.5%) 10-year risk for ASCVD with ASCVD risk-enhancing factors.
According to the ACC/AHA cholesterol guidelines, CAC scoring may also be reasonable (Class of Recommendation IIb) in older patients (76-80 years) with an LDL-C level of 70 to 189 mg/dL; if the CAC score is 0, statin therapy can be avoided. [Grundy SM, et al. J Am Coll Cardiol. 2018;26a]
Screening for CAC in low-risk populations will inevitably result in occasional false positives and screening high-risk populations is not recommended since aggressive risk factor reduction should already be taking place in these individuals. Identifying CAC in intermediate-risk populations allows the clinician to not only educate the patient regarding their ASCVD risk, but also to be more aggressive in the use of statin therapy to reduce the risk for adverse ASCVD events.
In contrast to the ACC/AHA guidelines, which only consider CAC scoring appropriate for selected intermediate-risk patients, the American College of Radiologists (ACR) Appropriateness Criteria consider CAC scoring potentially appropriate in asymptomatic patients at high risk for ASCVD. [Ghoshhajra BB, et al. J Am Coll Radiol. 2021;10a] Although these patients will be on lipid-lowering therapy per the ACC/AHA guidelines, the ACR recommendation is based on the potential for further risk assessment; high-risk patients with a CAC score of 0 may have a lower ASCVD event risk than high-risk patients with a higher CAC score.