How should a coronary artery calcium (CAC) score obtained by non‑contrast computed tomography (CT) be interpreted and what primary‑prevention management is recommended for each score category (0, 1–99, ≥100)?

Coronary Artery Calcium Score Interpretation and Management

Direct Answer

For asymptomatic adults aged 40-75 with intermediate or borderline cardiovascular risk, a CAC score of 0 indicates excellent prognosis with <1% annual event risk and allows deferral of statin therapy, a score of 1-99 warrants consideration of moderate-intensity statins especially if ≥75th percentile for age/sex, and a score ≥100 mandates moderate-to-high intensity statin therapy with aggressive risk factor modification. 1

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CAC Score Categories and Risk Stratification

CAC Score = 0 (Zero Calcium)

Risk Profile:

• Annual risk of cardiac death or myocardial infarction <1% (0.16%/year) 1
• 10-year cardiovascular event rate of only 0.47% in asymptomatic adults 1
• Strongest negative predictive factor for cardiovascular disease 2

Management:

• Statin therapy can be deferred if desired by the patient, as event rates fall below the 7.5% threshold where statin benefit is established 3
• Continue lifestyle modifications: Mediterranean or DASH diet, 150 minutes weekly moderate-intensity exercise, smoking cessation, weight management 4
• Blood pressure target <130/80 mmHg 4
• Repeat CAC scanning in 5 years (not sooner) if ongoing risk factors present, such as diabetes, smoking, chronic inflammatory disease, or strong family history of premature CAD 1, 5

Important Caveat:

• A CAC score of 0 does not exclude non-calcified plaque, which may be present in earlier stages of atherosclerosis 1
• In symptomatic patients, 3.5% with CAC=0 still had ≥50% stenosis and 1.4% had ≥70% stenosis, so zero calcium does not rule out obstructive disease when symptoms are present 1

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CAC Score = 1-99 (Mild Atherosclerosis)

Risk Profile:

• Presence of atherosclerosis with incrementally increased risk above zero 1
• 10-year cardiovascular risk approximately 7.4% in intermediate-risk individuals (compared to 1.5% with CAC=0) 1
• Low to low-moderate risk category (<10% 10-year risk) 5

Management:

• Consider moderate-intensity statin therapy, especially if score is ≥75th percentile for age/sex/race 1
• Intensify lifestyle modifications (diet, exercise, smoking cessation, weight management) 1
• Blood pressure control targeting <130/80 mmHg 4
• Low-dose aspirin may be considered, though evidence is less robust than for statins 4
• Repeat CAC scanning in 3-5 years to assess progression, which may support intensification of preventive management 1

Number Needed to Treat:

• 5-year NNT to prevent one ASCVD event: 154 in patients with CAC=0 and lipid abnormalities, versus 30 when CAC ≥100 even without lipid abnormalities 3

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CAC Score = 100-399 (Moderate Atherosclerosis)

Risk Profile:

• Indicates ≥7.5% 10-year ASCVD risk regardless of demographic subset 1
• Intermediate to moderately-high risk (10-20% 10-year cardiovascular event rate) 1, 5
• Relative risk 2.7-4.1 times higher for hard coronary events compared to zero calcium 4

Management:

• Initiate moderate-to-high intensity statin therapy immediately, targeting ≥30-50% LDL-C reduction 1, 4
• Blood pressure control <130/80 mmHg 4
• Consider low-dose aspirin, particularly when score >100 and above 75th percentile for age/sex 1, 5
• Aggressive lifestyle modification (Mediterranean diet, regular exercise, smoking cessation) 4
• Optimize glycemic control in diabetic patients 1

Number Needed to Treat:

• 5-year NNT to prevent one ASCVD event: approximately 30-42 1, 4
• 10-year NNT: 28 for CAC >100 in intermediate-to-high risk patients 3

Functional Testing:

• Stress testing is not routinely indicated unless symptoms develop or CAC exceeds 400 1, 4

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CAC Score ≥400 (Extensive Atherosclerosis)

Risk Profile:

• Extensive atherosclerotic burden with 7.2-fold to 10.8-fold increased risk of coronary heart disease death or myocardial infarction compared to CAC=0 1
• High risk (>20% 10-year event rate) 5
• Very high-risk category warranting aggressive preventive therapy 1

Management:

• High-intensity statin therapy is mandatory, targeting ≥50% LDL-C reduction 1, 4
• Blood pressure control <130/80 mmHg 4
• Low-dose aspirin after evaluating individual bleeding risk 1
• Comprehensive risk factor modification (diet, exercise, smoking cessation, diabetes optimization) 4

Functional Testing:

• Screening for clinically silent ischemia is warranted when CAC >400 (Class IIb recommendation from 2010 ACC/AHA guidelines) 1, 4
• Stress myocardial perfusion imaging (nuclear SPECT or PET) is the preferred first-line functional test, offering high diagnostic accuracy 1, 4
• Stress echocardiography is an acceptable alternative 4
• Avoid coronary CT angiography in patients with extensive calcification due to false-positive results from heavy calcium 4

Important Limitation:

• High CAC reflects overall atherosclerotic burden, not the degree of luminal narrowing; only ≈20% of total atherosclerosis is calcified, and arterial remodeling often preserves lumen patency 4
• CAC alone should not dictate revascularization decisions or replace functional testing when stenosis assessment is required 4

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Special Clinical Scenarios

Elevated Lipoprotein(a) with CAC Scoring

• Order CAC scoring in patients with elevated Lp(a) >50 mg/dL (>125 nmol/L) who fall into intermediate or borderline 10-year ASCVD risk categories where statin therapy decisions are uncertain 1
• CAC and Lp(a) provide independent prognostic information; their joint elevation identifies very high-risk patients requiring aggressive preventive therapy 1

Repeat CAC Scanning Intervals

• CAC = 0: Repeat in 5 years (not sooner), particularly if ongoing risk factors such as diabetes, smoking, or family history are present 1, 5
• CAC = 1-99: Repeat in 3-5 years if results might change treatment decisions 1
• CAC ≥400: Limited value in repeat scanning, as patients are already at high risk 3
• Average time to convert from CAC=0 to CAC>0 is 4.1±0.9 years; diabetes, age >40 years, and smoking are significant predictors for progression 3

Statin Therapy Effects on CAC

• Prolonged statin therapy may have procalcific effects on coronary atheromas and can increase CAC 3
• Interpretation of serial CAC should account for statin therapy effects 3
• CAC progression defined as >15% annualized change is associated with >3-fold increase in all-cause mortality 3

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Common Pitfalls and Caveats

When NOT to Order CAC Scoring

1. Symptomatic patients with chest pain or known CAD: CAC=0 does not exclude obstructive disease (7-38% of symptomatic patients with CAC=0 have obstructive CAD) 1
2. Low-risk asymptomatic patients (<5% 10-year ASCVD risk): Test does not provide actionable information that changes management 1
3. Men <40 years and women <50 years: Low prevalence of calcification in younger individuals 1
4. Patients already on high-intensity statins: CAC scoring unlikely to change management 3

CAC Score Limitations

• Does not detect non-calcified plaque, which may represent more vulnerable, rupture-prone lesions 1, 6
• Poor specificity (≈50%) for predicting obstructive coronary stenosis due to modest relationship between calcification and luminal obstruction 1, 4
• Should be seen primarily as a marker of atherosclerosis, not degree of stenosis 1, 6
• In certain metabolic conditions (diabetes, uremia), medial calcification may occur that does not reflect intimal atherosclerotic disease 4

Incidental Findings

• Nonvascular incidental findings occur in 0.4-16.5% of scans (lung nodules), with lung cancer detected in 0.0-1.2% 1
• These findings may create patient anxiety and trigger additional follow-up testing 1

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Technical Considerations

Ordering the Test

• Order as "CT Coronary Artery Calcium Score" or "Cardiac CT for Calcium Scoring" using ECG-gated multidetector computed tomography without contrast 1
• Radiation exposure is relatively low (0.37-1.5 mSv), comparable to 1-2 mammograms per breast 1
• Cost typically <$100 at many imaging centers 1

Insurance Coverage

• Not all insurance payors cover CAC scoring, as it is considered preventive screening rather than diagnostic imaging 1
• Medicare does not routinely cover CAC scoring for screening purposes 1
• Most commonly used ICD-10 code: Z13.6 (encounter for screening for cardiovascular disorders) 1