What information can be obtained from a coronary artery calcium (CAC) scan?

What You Can Learn from a Coronary Artery Calcium Scan

A coronary artery calcium (CAC) scan quantifies calcified atherosclerotic plaque burden in your coronary arteries and serves as one of the strongest independent predictors of future cardiovascular events, but it does NOT tell you whether you have obstructive coronary artery disease or whether specific blockages are causing symptoms. 1, 2

Primary Information Obtained

Atherosclerotic Burden Assessment

• CAC scanning definitively establishes the presence of coronary atherosclerosis, as calcification occurs exclusively in atherosclerotic lesions of the intimal layer and never in normal vessel walls 1, 2, 3
• The scan quantifies total calcified plaque burden using the Agatston scoring system, which measures lesions with CT density >130 Hounsfield units and area >1 mm² 1, 3
• The degree of calcification correlates with total atherosclerotic burden, though the CAC score represents only approximately 20% of total plaque burden since not all plaques contain calcium 1

Cardiovascular Risk Stratification

• CAC scoring provides robust risk prediction for future cardiovascular events including myocardial infarction, stroke, heart failure, atrial fibrillation, and cardiovascular death 1, 2, 4, 5
• Risk increases proportionally with calcium scores: adjusted relative risks escalate at thresholds of 11-100,101-400,401-1,000, and >1,000 1, 3
• A calcium score of zero indicates excellent prognosis with very low risk (<1% annually) for cardiac death or myocardial infarction 1, 2, 6
• CAC provides incremental prognostic information beyond traditional risk factors like the Framingham Risk Score 1, 7

Critical Limitations You Must Understand

What CAC Does NOT Tell You

• CAC scoring should be seen primarily as a marker of atherosclerosis and NOT as an indicator of stenosis degree or luminal obstruction 1, 2, 6
• The scan has poor specificity for diagnosing obstructive coronary artery disease due to modest correlation between calcification and arterial narrowing 1, 3
• In symptomatic patients with zero calcium score, 3.5% still had ≥50% arterial stenosis and 1.4% had ≥70% stenosis 3
• CAC cannot detect non-calcified atherosclerotic plaques, which may be present in earlier stages of disease 1, 3, 6
• Coronary calcifications are NOT indicators of plaque stability or instability 2

Functional Significance Cannot Be Determined

• A high calcium score does NOT necessarily indicate myocardial ischemia—one study showed that even with CAC scores of 1-399, only 21.7% had abnormal perfusion imaging, and 16% of patients with zero CAC still had ischemia on provocative testing 1
• Estimated stenoses between 50-90% by visual inspection are not necessarily functionally significant and do not always induce myocardial ischemia 2
• Lumen patency is often preserved by vascular remodeling, with limited correlation between calcium burden and residual luminal areas 1

Additional Information Beyond the Agatston Score

Plaque Characteristics

• Newer AI-enabled analysis can extract additional data including number of calcified plaques, their location, density, spatial distribution, and number of vessels involved 4, 5, 8
• These AI-enhanced measurements (AI-CAC) significantly improve cardiovascular event prediction compared to Agatston score alone, with AUCs of 0.816 vs 0.729 at 15-year follow-up 4, 5

Cardiac Chamber Information

• CAC scans can provide automated cardiac chamber volumetry when analyzed with AI algorithms 4, 5
• This additional information improves prediction of non-coronary events like heart failure and atrial fibrillation 5

Clinical Context for Appropriate Use

Best Used For

• Risk stratification in asymptomatic adults aged 40-75 years with intermediate (7.5-20%) or borderline (5-7.5%) 10-year ASCVD risk 1, 2, 3, 6
• Guiding decisions about preventive therapy (particularly statin therapy) when uncertainty exists 1, 2
• Reclassifying intermediate-risk patients without calcification into lower-risk groups, potentially avoiding unnecessary medications 1, 2

NOT Appropriate For

• Symptomatic patients with chest pain or known CAD, as CAC=0 does not exclude obstructive disease 3
• Men under 40 and women under 50 years due to low prevalence of calcification 3, 6
• As a surrogate for angiographic disease detection 1, 3
• Routine screening in asymptomatic individuals outside the intermediate-risk category 2

Common Pitfalls to Avoid

• Do not assume a high calcium score means you need invasive angiography—invasive coronary angiography is not recommended solely for risk stratification in asymptomatic patients regardless of calcium score (Class III recommendation) 2
• Do not assume zero calcium means no atherosclerosis—non-calcified plaques are not detected by non-contrast CT 2, 3
• Do not use CAC scoring to diagnose the cause of chest pain—symptomatic patients require functional testing or coronary CT angiography, not calcium scoring alone 1, 2
• In symptomatic patients with high calcium scores and uncertain functional significance on CT angiography, functional imaging (perfusion scintigraphy, stress echo, or cardiac MRI) is needed to determine if ischemia is present 1, 2