Coronary Calcium Score: Diagnostic Test Classification
A coronary calcium score is a non-invasive imaging test that quantifies coronary artery calcification using computed tomography (CT) to assess atherosclerotic plaque burden and predict cardiovascular risk—it is fundamentally a risk stratification tool, not a diagnostic test for obstructive coronary artery disease. 1, 2
What the Test Actually Measures
Coronary CT detects and quantifies coronary artery calcium (CAC), which serves as a marker of total atherosclerotic disease burden and vascular age. 1, 2
The scan uses electrocardiogram-gated multidetector CT (or electron beam tomography) with relatively low radiation exposure of approximately 0.37-1.5 mSv—comparable to 1-2 mammograms per breast. 1, 3
The Agatston score is the most widely used quantification method, defining calcific lesions as having CT density >130 Hounsfield units with area >1 mm². 2, 4
Calcification does not occur in normal vessel walls, so any detectable calcium definitively confirms the presence of atherosclerosis. 1, 2
Critical Distinction: Atherosclerosis vs. Stenosis
CAC scoring has only ~50% specificity for detecting ≥50% luminal stenosis because calcium burden reflects total plaque burden, not the degree of luminal obstruction. 1, 2
The test cannot detect non-calcified atherosclerotic plaques, which may be present in earlier disease stages and can be clinically significant. 1, 2, 3
Coronary calcification is neither a marker of plaque stability nor instability—it simply indicates atherosclerotic burden. 1, 5
Patients with acute coronary syndromes often have extensive coronary calcification, but the calcium itself does not predict which specific plaque will rupture. 1, 5
Primary Clinical Role: Risk Stratification
CAC scoring is most appropriately used for cardiovascular risk assessment in asymptomatic adults aged 40-75 years with intermediate (7.5-20%) or borderline (5-7.5%) 10-year ASCVD risk when preventive treatment decisions are uncertain. 1, 2, 3
A CAC score of zero indicates excellent prognosis with very low risk (<1% annually) for cardiac death or myocardial infarction, allowing potential deferral of statin therapy. 2, 3, 6
Cardiovascular risk increases proportionally with calcium scores, with scores ≥400 indicating high risk (>20% 10-year event rate) and warranting aggressive preventive therapy. 2, 5, 6
The test provides incremental prognostic information beyond conventional risk factors like Framingham Risk Score. 6, 7
When NOT to Use CAC Scoring
CAC scoring should not be ordered to diagnose or exclude obstructive coronary artery disease in symptomatic patients because 7-38% of symptomatic patients with CAC=0 still have obstructive CAD. 2
The test was explicitly not recommended in the 2000 ACC/AHA expert consensus document to diagnose obstructive CAD due to its low specificity for stenosis detection. 1
For symptomatic patients requiring stenosis assessment, functional stress testing (stress myocardial perfusion imaging, stress echocardiography) or coronary CT angiography are appropriate first-line tests. 2
CAC scoring should not be used to determine need for revascularization or replace invasive coronary angiography when definitive stenosis assessment is needed. 2
Common Clinical Pitfall
The most frequent misunderstanding is interpreting CAC scoring as a test for coronary stenosis. A high calcium score (e.g., 400) indicates extensive atherosclerotic burden and high cardiovascular risk, but does NOT confirm the presence of flow-limiting stenoses requiring revascularization. 1, 2 Conversely, a zero calcium score provides excellent negative predictive value for excluding significant stenosis in asymptomatic patients, but this warranty diminishes in symptomatic individuals and those with diabetes beyond 5 years. 1, 2