When to Order Coronary Artery Calcium Score
Order coronary artery calcium (CAC) scoring for asymptomatic adults aged 40-75 years with intermediate (7.5-20%) or borderline (5-7.5%) 10-year ASCVD risk when the decision about initiating statin therapy remains uncertain after initial risk assessment. 1, 2
Primary Clinical Algorithm
Step 1: Calculate 10-Year ASCVD Risk
- Use the ACC/AHA Pooled Cohort Equations for patients aged 40-75 years with LDL-C 70-189 mg/dL 2, 3
- Verify the patient meets age criteria: minimum 40 years for men, 50 years for women (due to low prevalence of detectable calcium in younger individuals) 2, 3
Step 2: Risk-Based Decision Framework
High Risk (≥20% 10-year ASCVD risk):
- Do NOT order CAC scoring—statin therapy is already indicated regardless of CAC results 2, 3
- Initiate high-intensity statin immediately 3
Intermediate Risk (7.5-19.9% 10-year ASCVD risk):
- This is the strongest indication for CAC scoring 1, 2, 3
- Order CAC when uncertainty persists after discussing statin benefits, risks, and patient preferences 2, 3
- Exception: Active smokers should receive moderate-intensity statin immediately without waiting for CAC results, as smoking overrides a CAC=0 result 3
Borderline Risk (5-7.4% 10-year ASCVD risk):
- Consider CAC scoring when risk-enhancing factors are present: 1, 2, 3
- Family history of premature CAD
- Elevated lipoprotein(a) >50 mg/dL (>125 nmol/L)
- Metabolic syndrome
- Chronic inflammatory conditions (rheumatoid arthritis, psoriasis, HIV)
- Chronic kidney disease
- Persistently elevated LDL-C ≥160 mg/dL
Low Risk (<5% 10-year ASCVD risk):
- Do NOT order CAC scoring—the test does not provide actionable information and exposes patients to unnecessary radiation 2, 3
- Exception: May consider in patients <40 years with strong family history of premature CAD, though this falls outside standard guidelines 2
Special Populations
Diabetes Mellitus:
- Consider CAC in younger diabetic patients (Type 1 DM <35 years, Type 2 DM <50 years) with diabetes duration <10 years and no other major risk factors for risk stratification 1, 3
Elderly Patients (76-80 years):
- CAC scoring may be reasonable only to reclassify patients with CAC=0 to avoid statin therapy in those with LDL-C 70-189 mg/dL 4
- Beyond age 80, CAC scoring is NOT recommended—treatment decisions should be based on functional status, life expectancy, and patient preferences 4
Patients Refusing Statin Therapy:
- CAC may be indicated when high-risk patients refuse recommended statin therapy, as a CAC >100 may motivate adherence 3
Interpreting CAC Results for Management
| CAC Score | 10-Year Event Rate | Management Recommendation |
|---|---|---|
| 0 | 1.5-3.0% | Defer statin therapy in most cases; reassess in 5-10 years [2,3] |
| Exception: Do NOT defer in active smokers, diabetics, or those with family history of premature CAD [3] | ||
| 1-99 | 6.5-7.4% | Initiate moderate-intensity statin, especially if age ≥55 years [2,3] |
| ≥100 or ≥75th percentile | ≥20 per 1,000 person-years | Initiate moderate-to-high intensity statin [2,3] |
| ≥300 | Very high risk | Initiate high-intensity statin (≥50% LDL-C reduction) [2,3] |
Critical Pitfalls to Avoid
Do NOT order CAC in symptomatic patients:
- CAC scoring reflects atherosclerotic burden, NOT degree of stenosis 2
- 7-38% of symptomatic patients with CAC=0 have obstructive CAD 2
- Symptomatic patients require functional testing (stress imaging) or coronary CT angiography instead 2
Active smoking overrides CAC=0:
- Never defer statin therapy in current smokers based on CAC=0 3
- Smoking is a powerful risk-enhancing factor that raises actual ASCVD risk beyond calculated estimates 3
- Initiate moderate-intensity statin and aggressive smoking cessation counseling immediately 3
Do NOT repeat CAC too soon:
- Avoid repeating CAC within 3-5 years for patients already on optimal therapy 2, 3
- For initial CAC=0, repeat scanning after 5-10 years is reasonable 2, 3
Insurance and cost considerations:
- Medicare does not routinely cover CAC scoring for screening purposes 2
- Typical cost is <$100 at many imaging centers, but insurance may deny claims for inappropriate indications 2
Technical Specifications
- Order as "CT Coronary Artery Calcium Score" or "Cardiac CT for Calcium Scoring" 2
- Uses ECG-gated multidetector computed tomography without contrast 2
- Radiation exposure is relatively low (0.37-1.5 mSv), equivalent to 1-2 mammograms per breast 2, 3
- Agatston score is the standard method, defining calcific lesions as CT density >130 Hounsfield units with area >1 mm² 2
What CAC Does NOT Tell You
- CAC quantifies atherosclerotic plaque burden, not luminal narrowing 2
- Only 20% of total atherosclerosis burden contains calcium—non-calcified plaques are completely missed 2
- Poor correlation with degree of stenosis due to vascular remodeling 2
- Cannot detect vulnerable plaques or assess plaque stability 2