For an asymptomatic adult aged 40‑75 years without known atherosclerotic cardiovascular disease and a 10‑year ASCVD risk of 5‑20 %, when is a coronary artery calcium (CAC) scan indicated?

Guidelines for Ordering Coronary Artery Calcium (CAC) Scoring

For asymptomatic adults aged 40–75 years with a 10-year ASCVD risk of 5–20%, CAC scoring is indicated when uncertainty persists about initiating statin therapy after a structured risk discussion, with the strongest evidence supporting its use in the intermediate-risk range (7.5–20%). 1

Primary Indications by Risk Category

Intermediate Risk (7.5–20% 10-year ASCVD risk)

• Order CAC scoring when the decision about statin therapy remains uncertain after discussing risks, benefits, and patient preferences. This is the most evidence-based indication, with CAC providing the most reliable means of clarifying risk in this population. 2
• Nearly one-fifth of US adults aged 45–79 years fall into this intermediate-risk category, where patients are often reluctant to begin statin therapy due to concerns about side effects and uncertain benefit. 2
• CAC is superior to all other nontraditional markers (carotid intimal thickness, ankle-brachial index, C-reactive protein) for predicting ASCVD risk in this population. 2

Borderline Risk (5.0–7.4% 10-year ASCVD risk)

• Order CAC scoring when one or more risk-enhancing factors are present, including premature family history of CAD, elevated lipoprotein(a), metabolic syndrome, chronic inflammatory disease, chronic kidney disease, or LDL-C ≥160 mg/dL. 1
• This represents a reasonable use of CAC to establish the presence of atherosclerosis and guide decisions about preventive therapy. 2

Low Risk (<5% 10-year ASCVD risk)

• Do not order CAC scoring in truly low-risk patients without risk-enhancing factors. The radiation exposure (approximately 1.5 mSv) cannot be justified when pretest probability is very low. 3
• Even family history alone, without other risk factors or elevated lipids, is insufficient indication for CAC scoring in patients with calculated risk <5%. 3

High Risk (≥20% 10-year ASCVD risk)

• Do not order CAC scoring—statin therapy is already indicated regardless of CAC results. CAC adds no value to treatment decisions in this population. 1

Age-Specific Considerations

Ages 40–75 Years

• This is the validated age range for CAC scoring across all major guidelines, corresponding to the age range of the ASCVD Pooled Cohort Equations. 4
• Age ≥40 years is the minimum threshold for CAC scoring. 1

Ages 76–80 Years

• CAC scoring may be considered only to support deferring statin therapy in patients with LDL-C 70–189 mg/dL when a CAC score of zero would definitively change the decision. This is a narrow indication for highly selected patients. 4

Age >80 Years

• Do not order CAC scoring—it is beyond the validated age range of risk calculators. Treatment decisions should be based on functional status, life expectancy, and patient preferences rather than CAC results. 4

Special Populations

Younger Diabetic Patients

• Consider CAC scoring in Type 1 diabetes <35 years or Type 2 diabetes <50 years with disease duration <10 years and no other major risk factors. This helps identify subclinical atherosclerosis in patients who may not meet traditional intermediate-risk thresholds. 1

Patients Refusing Recommended Therapy

• Consider CAC scoring when high-risk patients refuse recommended statin therapy, as a CAC >100 may motivate adherence and shared decision-making. 1

Interpretation and Management Algorithm

CAC Score = 0 (No Detectable Calcium)

• Defer statin therapy in most intermediate-risk patients, as the annual cardiac death/MI risk is <1% (approximately 0.16%/year). 1
• Critical exception: Do not defer statin therapy in active smokers, diabetics, or patients with premature family history of CAD—these factors override the protective implication of a zero score. 1
• Repeat CAC in 5–10 years if risk factors persist. 1

CAC Score 1–99 (Mild Calcification)

• Initiate moderate-intensity statin therapy, especially in patients ≥55 years. The event rate rises to approximately 6.5–7.4%, representing meaningful upward risk reclassification. 1
• Target ≥30% LDL-C reduction. 1
• Consider repeat CAC in 3–5 years if results may change management. 1

CAC Score 100–399 (Moderate Calcification)

• Initiate moderate-to-high-intensity statin therapy. This score corresponds to ≥7.5% 10-year ASCVD risk across all demographics, with event rates approximating secondary-prevention cohorts (≥20 per 1,000 person-years). 1
• Target 30–50% LDL-C reduction based on overall risk. 1

CAC Score ≥400 (Extensive Calcification)

• Initiate high-intensity statin therapy with ≥50% LDL-C reduction. The risk of coronary death/MI is 7.2- to 10.8-fold higher than CAC = 0. 1
• For CAC ≥1,000, the need for high-intensity therapy is especially critical. 1

Aspirin Consideration

• Consider low-dose aspirin (81 mg daily) for CAC ≥100 after individualized bleeding-risk assessment, with stronger consideration when CAC ≥300. 1

Critical Pitfalls to Avoid

Active Smoking

• Active smoking overrides a CAC = 0 result—do not defer statin therapy in current smokers. Smoking is a powerful risk-enhancing factor that raises actual ASCVD risk beyond the calculated estimate. 1
• Initiate moderate-intensity statin promptly and prioritize smoking-cessation counseling alongside lipid management. 1

Inappropriate Repeat Imaging

• Do not repeat CAC imaging within 3–5 years in patients already on optimal therapy—progression is expected and does not indicate treatment failure. 1
• For an initial CAC = 0, repeat scanning after 5–10 years is reasonable if risk factors persist. 1

Misinterpretation of CAC as Stenosis Marker

• CAC quantifies atherosclerotic burden, not luminal stenosis. Only approximately 20% of total atherosclerotic plaque contains calcium, so CAC cannot rule in or rule out coronary artery stenosis. 1
• Lumen patency is often preserved by vascular remodelling, with limited correlation between residual luminal areas and calcified areas. 2

Use in Symptomatic Patients

• Do not use CAC scoring in symptomatic patients—a zero CAC does not exclude obstructive CAD; functional testing or coronary CTA is preferred in this population. 5

Practical Clinical Algorithm

Step 1: Calculate 10-year ASCVD risk using the ACC/AHA Pooled Cohort Equations for adults aged 40–75 years with LDL-C 70–189 mg/dL. 1

Step 2: Apply risk-based treatment thresholds:

• High risk (≥20%): Start high-intensity statin immediately; CAC scoring is unnecessary. 1
• Intermediate risk (7.5–19.9%): Conduct a structured discussion of statin benefits (approximately 20–30% relative risk reduction) and patient preferences. If uncertainty persists, obtain CAC scoring. 1
• Borderline risk (5.0–7.4%): If risk-enhancing factors are present, consider CAC scoring to guide therapy decisions. 1
• Low risk (<5%): Do not order CAC unless a strong family history of premature CAD exists. 3

Step 3: Interpret CAC results and initiate therapy according to the score-specific recommendations above. 1

Step 4: Address concurrent risk factors:

• Smoking cessation provides cardiovascular benefit equal to or greater than statin therapy and must be addressed aggressively. 1
• Uncontrolled hypertension should be treated concurrently with lipid-lowering strategies. 1

Radiation Exposure Context

• The CACS radiation dose is relatively small (0.37 ± 0.16 mSv), slightly lower than screening mammography (0.44–0.56 mSv). 2
• This low radiation exposure is acceptable in intermediate-risk patients where CAC results will meaningfully alter management, but not justified in low-risk patients where treatment decisions are unlikely to change. 3