Order a Coronary Artery Calcium (CAC) Score CT Scan
For a patient with mildly elevated cholesterol requesting a CAC score, you should order a non-contrast, ECG-gated cardiac CT scan for coronary artery calcium scoring 1, 2.
What to Order Specifically
Order: "Non-contrast ECG-gated cardiac CT for coronary artery calcium scoring (Agatston score)"
- This is a dedicated cardiac CT scan, not a regular chest CT
- No IV contrast is required
- The scan is ECG-gated to acquire images during mid-diastole when the heart is most still
- Radiation exposure is minimal (approximately 0.37-1 mSv), comparable to or less than screening mammography 2
- Results will be reported as an Agatston score with age/sex/race-adjusted percentiles 2
When CAC Scoring is Most Appropriate
Before ordering, calculate the patient's 10-year ASCVD risk using the ACC/AHA Pooled Cohort Equation or MESA calculator 2. CAC scoring is most valuable for:
Primary Indications 1, 2:
- Intermediate risk patients (7.5%-20% 10-year ASCVD risk) where statin decision is uncertain
- Borderline risk patients (5%-7.5% 10-year ASCVD risk) with risk-enhancing factors where treatment decision remains unclear
Risk-Enhancing Factors to Consider 1:
- Family history of premature ASCVD
- Persistently elevated LDL-C ≥160 mg/dL or triglycerides ≥175 mg/dL
- Chronic kidney disease
- Metabolic syndrome
- Inflammatory conditions (rheumatoid arthritis, psoriasis, HIV)
- High-risk ethnicity (South Asian)
- Elevated hs-CRP ≥2.0 mg/L or Lp(a) >50 mg/dL (if measured)
How Results Will Guide Management
The CAC score will directly inform statin therapy decisions 1, 2:
CAC = 0 (45% of patients with elevated cholesterol) 3:
- Downgrade risk - consider withholding statin therapy
- 10-year event rate only 1.5-4.6% even in intermediate risk patients 2
- Exception: Still consider statin if diabetes, family history of premature CAD, or active smoking present 1
- Repeat CAC in 3-7 years 1
CAC = 1-99:
CAC ≥100 or ≥75th percentile:
- Initiate statin therapy 1, 2
- Consider high-intensity statin
- May add aspirin 81 mg daily 1
- 10-year event rate 10.4% in intermediate risk patients 2
Important Caveats
Do NOT order CAC scoring if 2:
- Patient has known coronary artery disease - CAC has no value and is explicitly discouraged by ACC/AHA guidelines and Choosing Wisely 4
- Patient is symptomatic with chest pain - CAC = 0 does not exclude obstructive disease in symptomatic patients (19-38% may still have significant stenosis) 2
- Patient is low risk (<5% 10-year ASCVD) or high risk (≥20%) - CAC won't change management in these groups 2
Key Clinical Pitfall: CAC detects only calcified plaque, representing approximately 20% of total atherosclerotic burden 2. Non-calcified plaque is not visualized, so CAC = 0 indicates low but not zero risk.
Cost-Effectiveness
CAC scoring is most cost-effective in intermediate-risk patients 2:
- Number needed to treat (NNT) with statins to prevent one ASCVD event over 5 years: 154 for CAC = 0 vs 30 for CAC ≥100
- Over half of borderline and intermediate-risk patients can be reclassified as low risk if CAC = 0, avoiding unnecessary statin therapy and costs 2
The test is typically self-pay (not covered by insurance), so ensure the patient understands this will likely be an out-of-pocket expense and that results will meaningfully impact treatment decisions 5.