What are the guidelines for a coronary calcium CT scan in adults with risk factors for coronary artery disease?

Guidelines for Coronary Artery Calcium CT Scan

Coronary artery calcium (CAC) scoring is most appropriate 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 disease risk when decisions about preventive interventions like statin therapy are uncertain. 1

Primary Indications for CAC Scoring

Risk-Based Patient Selection

• Intermediate-risk patients (≥7.5% to <20% 10-year ASCVD risk) represent the strongest indication, as CAC scoring provides Class IIa recommendation (reasonable guide for shared decision-making) with Level B-NR evidence from the 2019 ACC/AHA guidelines 1

• **Borderline-risk patients (5% to <7.5% 10-year ASCVD risk)** may be considered for CAC scoring when risk-enhancing factors are present, such as family history of premature CAD, metabolic syndrome, chronic inflammatory conditions, or elevated lipoprotein(a) >50 mg/dL 1

• Selected low-risk patients (<5% 10-year risk) with strong family history of premature coronary heart disease may be considered, though this represents a weaker indication 1

Age Requirements

• Minimum age of 40 years for men and 50 years for women due to low prevalence of detectable calcium in younger individuals 2
• Upper age limit of 75 years per most guidelines, though some evidence supports use in older adults 1

When CAC Scoring is NOT Appropriate

Absolute Contraindications

• Symptomatic patients with chest pain or angina should NOT receive CAC scoring, as 7-38% of symptomatic patients with CAC=0 still have obstructive coronary artery disease 1
• Known coronary artery disease patients do not benefit from CAC scoring 1
• Truly low-risk asymptomatic patients (<5% 10-year ASCVD risk) without risk-enhancing factors, as the test does not provide actionable information 2

Clinical Reasoning

The 2013 expert consensus on appropriate use criteria did not deem imaging for evaluating ischemic heart disease in asymptomatic low-risk patients to be appropriate 1

Technical Specifications

Ordering the Test

• Order as "CT Coronary Artery Calcium Score" or "Cardiac CT for Calcium Scoring" 2
• Uses ECG-gated multidetector computed tomography without contrast 1, 2
• Radiation exposure is relatively low (0.37-1.5 mSv), equivalent to 1-2 mammograms 1, 2

Scoring Method

The Agatston score is the standard method, defining calcific lesions as having CT density >130 Hounsfield units with area >1 mm² 1, 3

Interpretation and Risk Stratification

CAC Score Categories and Management

CAC = 0 (No Calcium)

• Indicates excellent prognosis with very low risk (<1% annually or 0.16%/year) for cardiac death or myocardial infarction 1
• Can successfully de-risk patients and potentially defer statin therapy 1, 4
• Critical caveat: Does NOT exclude non-calcified plaque or obstructive disease in symptomatic patients 1, 3

CAC = 1-99 (Minimal Calcium)

• Indicates presence of atherosclerosis with incrementally increased risk above zero 2
• Consider lifestyle modifications and potentially statin therapy, especially if score is ≥75th percentile for age/sex/race 1

CAC = 100-399 (Moderate Calcium)

• All patients in this category have ≥7.5% 10-year ASCVD risk regardless of demographic subset 1
• Statin therapy benefits clearly exceed potential harm 1
• Event rate approximates ≥20 events per 1000 person-years 1

CAC ≥ 400 (Severe Calcium)

• Indicates extensive atherosclerotic burden with 7.2-fold to 10.8-fold increased risk of coronary heart disease death or myocardial infarction compared to CAC=0 5
• Requires aggressive preventive therapy including high-intensity statins 5
• The 2010 AHA/ACC guidelines gave Class IIb recommendation to test for clinically silent ischemia in asymptomatic patients with CACS > 400 1

Repeat Scanning Intervals

Evidence-Based Timing

For CAC = 0:

• Repeat in 5-10 years for low-risk individuals 1
• ESC guidelines recommend not repeating <5 years from initial scan 1
• Canadian guidelines do not recommend repeat scans unless personal risk factors change or pharmacotherapy is deferred 1

For CAC = 1-99:

• NLA recommends repeat in 3-5 years if results might change treatment decisions 1
• SCCT recommends every 3-5 years when CAC progression would support intensification of preventive management 1

For CAC = 100-400:

• CSANZ recommends repeat at 3 years for diabetic patients 1
• NLA recommends 3-5 years for borderline- to intermediate-risk patients 1

For CAC > 400:

• May not require repeat CAC screening as these patients are already high-risk and vigorously treated 1

Special Populations

Younger Adults (Age 30-49)

• More than 34% of young adults have CACS > 0, and 7.2% have CACS > 100 with 10-fold higher CAD-related mortality 1
• CAC presence increases risk for CAD events by 3- to 12-fold compared to those without CAC 1
• May have potential benefit in select younger patients with risk factors (smoking, hyperglycemia, hyperlipidemia, hypertension) 1

Patients with Elevated Lipoprotein(a)

• CAC scoring is the most accurate tool for cardiovascular disease risk assessment when treatment decisions are uncertain in patients with elevated Lp(a) >125 nmol/L (50 mg/dL) 2
• CAC and Lp(a) provide independent prognostic information, and their joint elevation identifies very high-risk patients requiring aggressive preventive therapy 2

Important Limitations and Caveats

Clinical Limitations

• CAC scoring reflects atherosclerotic burden but does NOT directly assess degree of stenosis or plaque vulnerability 5
• Cannot detect non-calcified atherosclerotic plaque, which may be present in earlier stages of atherosclerosis 2, 3
• In symptomatic patients with CAC=0,19% had at least one ≥50% stenotic vessel, and 20% of occluded vessels had no CAC 1

Practical Considerations

• Not all insurance payors cover CAC scoring, and Medicare does not routinely cover it for screening purposes 2
• Nonvascular incidental findings (lung nodules in 0.4-16.5%, lung cancer in 0.0-1.2%) may create patient anxiety and trigger additional follow-up 1
• Lack of prospective randomized controlled trials evaluating effectiveness of CACS as a screening tool for improving cardiovascular outcomes 1

Downstream Testing After CAC Scoring

When Additional Testing May Be Reasonable

• Additional noninvasive testing (stress echocardiography, nuclear myocardial perfusion imaging, MRI, or coronary CT angiography) may be reasonable for patients with CAC in whom functional capacity cannot be reliably estimated 1
• For CAC scores >200-400, consider stress testing or advanced imaging to assess for myocardial ischemia, particularly if symptoms or additional high-risk features are present 2
• Approximately 48.5% of patients with CAC scores >400 have abnormal perfusion on imaging 5