When should a Coronary Artery Calcium (CAC) score be ordered for patients with risk factors for cardiovascular disease?

When to Order Coronary Artery Calcium (CAC) Score

CAC scoring should primarily be ordered for asymptomatic adults aged 40-75 years with intermediate ASCVD risk (7.5-20% 10-year risk) or borderline risk (5-7.5% 10-year risk) when decisions about preventive interventions remain uncertain. 1

Primary Indications for CAC Scoring

Recommended Populations:

• Intermediate risk patients (7.5-20% 10-year ASCVD risk)

  • Ages 40-75 years
  • No known coronary artery disease
  • When statin decision is uncertain 1

• Borderline risk patients (5-7.5% 10-year ASCVD risk)

  • Selected adults where preventive intervention decisions remain unclear 1

• Low risk patients (<5% 10-year risk) with specific risk enhancers:

  • Strong family history of premature CAD 1
  • South Asian ethnicity 1
  • Elevated high-sensitivity C-reactive protein or lipoprotein(a) 1

• Special populations:

  • Diabetic patients aged 40-60 years 1, 2
  • Patients with chronic kidney disease 1

Not Recommended For:

• Symptomatic patients (CAC=0 does not exclude obstructive CAD) 1
• Very low risk patients without risk enhancers 1
• High risk patients already requiring statin therapy 1
• Universal screening 3

Clinical Decision Algorithm Based on CAC Score

1. CAC = 0:

   • Downgrade risk assessment
   • Consider withholding statin (unless diabetes, family history of premature CAD, or active smoking) 1
   • Repeat CAC testing in 5-10 years 1

2. CAC = 1-99:

   • Favors statin therapy, especially after age 55 1
   • Consider moderate-intensity statin

3. CAC = 100-399:

   • Initiate statin therapy 1, 2
   • If score is above 75th percentile for age/sex, consider high-intensity statin and aspirin 2

4. CAC ≥ 400:

   • High risk classification
   • Initiate high-intensity statin and aspirin 1, 2
   • Consider more aggressive risk factor modification

Risk Reclassification Impact

CAC scoring significantly improves risk prediction compared to traditional risk factor equations, with:

• Improved discrimination (c-statistic from 0.784 to 0.817) 4
• Integrated discrimination improvement of 0.0252 4
• Net reclassification improvement of 0.121 4

Important Caveats and Considerations

• CAC scoring should only be undertaken if an alteration in therapy is being considered based on the test result 2
• Counsel patients thoroughly before ordering CAC testing about potential implications for treatment decisions 2
• The risk for adverse events is proportional to the score: higher scores indicate higher risk 1
• CAC=0 has excellent prognosis with event rate of 0.16%/year 1
• For diabetic patients or those with CAC 101-400, consider repeat CAC at 3 years 1
• Patients with high CAC scores (>400) may not require repeat CAC screening as they are often already vigorously treated 1

By following these guidelines, clinicians can appropriately utilize CAC scoring to refine cardiovascular risk assessment and make more informed decisions about preventive therapies, potentially improving morbidity and mortality outcomes through better targeted interventions.