Coronary Artery Calcium (CAC) Assessment in Intermediate Risk Patients
CAC scoring is strongly recommended for patients with intermediate risk (7.5% to <20% 10-year ASCVD risk) of coronary artery disease to guide decision-making regarding preventive therapy, particularly statin initiation. 1
Risk Stratification Using CAC
CAC scoring provides objective assessment of atherosclerotic burden and helps reclassify patients' risk levels, which is particularly valuable for intermediate-risk patients where clinical decision-making is often uncertain.
When to Order CAC:
- Primary indication: Asymptomatic patients with intermediate risk (7.5% to <20% 10-year ASCVD risk) 1
- Secondary indication: Borderline risk (5% to <7.5% 10-year ASCVD risk) patients 1
- Special populations that may benefit from CAC assessment:
- Patients with inflammatory disorders (rheumatoid arthritis, psoriasis, HIV) 1
- High-risk ethnic groups (e.g., South Asian) 1
- Patients with persistent triglyceride elevations >175 mg/dL 1
- Patients with family history of premature CAD 1
- Diabetic patients aged 40-60 years with lower risk profile (DM duration <10 years without additional risk factors) 1
When NOT to Order CAC:
- Low-risk patients (<5% 10-year risk) without family history of premature ASCVD 1
- High-risk patients (>20% 10-year risk) who should receive statin therapy regardless of CAC score 1
- Symptomatic patients (CAC is not validated for excluding obstructive CAD in symptomatic individuals) 1
- Patients with known coronary artery disease 2
- Patients with chronic kidney disease on dialysis 1
- Diabetic patients with long-standing disease (>10 years) or target organ damage 1
Interpreting CAC Scores and Clinical Decision-Making
CAC Score Categories and Risk:
| CAC Score | Risk Category | Treatment Recommendation |
|---|---|---|
| 0 | Very low risk | Consider deferring statin therapy [1,3] |
| 1-99 | Mildly increased risk | Moderate intensity statin if >75th percentile; otherwise consider lifestyle modification [1] |
| 100-299 | Moderately increased risk | Moderate to high intensity statin + ASA 81mg [1,3] |
| ≥300 | Moderate to severely increased risk | High intensity statin + ASA 81mg [1,3] |
Risk Reclassification:
CAC scoring significantly improves risk prediction beyond traditional risk factors:
- In the MESA study, inclusion of CAC improved the C-statistic from 0.76 to 0.81 (p<0.001) 1
- Approximately 57% of borderline and intermediate-risk patients with CAC=0 can be reclassified to lower risk, potentially avoiding unnecessary statin therapy 1
- Conversely, patients with elevated CAC scores have substantially higher event rates, warranting more aggressive therapy 1
Implementation in Practice
- Calculate 10-year ASCVD risk using the Pooled Cohort Equation for patients aged 40-75 years
- For intermediate-risk patients (7.5-<20%), consider CAC testing before initiating statin therapy
- Based on CAC results:
- CAC=0: Consider deferring statin therapy, focus on lifestyle modifications
- CAC 1-99: Consider moderate-intensity statin, especially if score >75th percentile for age/sex/race
- CAC 100-299: Initiate moderate to high-intensity statin therapy
- CAC ≥300: Initiate high-intensity statin therapy plus aspirin 81mg daily
Clinical Pitfalls to Avoid
- Don't rely on CAC to exclude CAD in symptomatic patients - CAC=0 doesn't rule out non-calcified plaque or significant stenosis 1
- Don't down-classify risk in diabetic patients with CAC=0 due to potential presence of non-calcified plaques 1
- Don't order CAC for patients with known CAD - this is discouraged by guidelines and the Choosing Wisely campaign 2
- Don't repeat CAC testing too frequently - appropriate intervals are 5-7 years for CAC=0,3-5 years for CAC 1-99, and 3 years for CAC≥100 3
By incorporating CAC assessment into risk stratification for intermediate-risk patients, clinicians can more accurately identify individuals who will benefit most from preventive therapies, improving outcomes while avoiding unnecessary treatment in those less likely to benefit.