How to Order a Coronary Artery Calcium Score
Order a coronary artery calcium (CAC) score as "CT Coronary Artery Calcium Score" or "Cardiac CT for Calcium Scoring" using ECG-gated multidetector computed tomography without contrast. 1, 2
Technical Specifications for the Order
The order should specify:
- Non-contrast cardiac CT scan with prospectively ECG-triggered scanning mode 3
- 2.5-3.0 mm thick axial images obtained through the heart 3
- Agatston scoring method (the most widely used scoring system, defining calcific lesions as having CT density >130 Hounsfield units and area >1 mm²) 2
- The scan uses relatively low radiation exposure (approximately 0.37-1.5 mSv), comparable to screening mammography 2, 3
Appropriate Patient Selection Before Ordering
Order CAC scoring for asymptomatic adults aged 40-75 years with intermediate (7.5-20% 10-year ASCVD risk) or borderline (5-7.5% 10-year ASCVD risk) cardiovascular risk when decisions about preventive interventions are uncertain. 1
Additional appropriate indications include:
- Selected low-risk adults with family history of premature CAD 1
- Patients where shared decision-making about statin therapy is needed 1
When NOT to Order CAC Scoring
Do not order CAC scoring for:
- Men under 40 and women under 50 years due to low prevalence of calcification in younger individuals 2, 3
- Symptomatic patients with chest pain or known CAD, as CAC=0 does not exclude obstructive disease (7-38% of symptomatic patients with CAC=0 have obstructive CAD) 1
- Patients already at high risk who clearly warrant statin therapy regardless of CAC score 4
- Patients at very low risk where management would not change 4
Critical Pre-Order Counseling
Only order CAC scoring if you are prepared to alter therapy based on the result - specifically, if you are considering starting or withholding statin therapy or aspirin based on the score. 4 The cost is typically borne entirely by the patient, so discuss implications before ordering. 4
Common Pitfalls to Avoid
- Do not order CAC as a surrogate for detecting obstructive disease - it is a marker of atherosclerotic burden, not stenosis severity 2
- Do not order both non-contrast and contrast CT - CAC can be measured from contrast-enhanced CT using a 320 Hounsfield unit threshold if needed, though non-contrast remains the standard 5
- Do not order repeat CAC sooner than 5 years in patients with CAC=0 4