In an asymptomatic adult, does a coronary calcium scoring CT detect non‑calcified (soft) plaque, or is coronary CT angiography required?

Coronary Calcium Scoring vs. CT Angiography for Non-Calcified Plaque Detection

Coronary calcium scoring CT cannot reliably detect non-calcified (soft) plaque—coronary CT angiography (CCTA) is required for this purpose. 1

What Calcium Scoring Actually Detects

• Calcium scoring exclusively quantifies calcified plaque burden using the Agatston method and provides no systematic assessment of non-calcified atherosclerotic plaque. 1, 2

• The American College of Radiology explicitly states that calcium score should not be used in isolation and must be combined with at least a qualitative assessment of total plaque burden (both calcified and non-calcified) to ensure non-calcified plaque is accounted for. 1, 2

• A calcium score of zero does NOT rule out the presence of non-calcified plaque, as confirmed by multiple guideline societies including the American College of Cardiology and American College of Radiology. 1, 2, 3

Why CCTA Is Required for Non-Calcified Plaque

• CCTA with intravenous contrast is the only non-invasive modality that allows assessment of both non-calcified and calcified plaque and can visualize resultant coronary stenosis. 1

• The American Heart Association guidelines emphasize that CCTA's greatest advantage is its high negative predictive value: if no evidence of either calcified or non-calcified (soft/fibrous) plaque is found, it is highly unlikely that symptoms are due to atherosclerotic coronary disease. 1

• CCTA can distinguish plaque composition based on CT density (Hounsfield units), with lowest density values correlating with lipid-laden plaque and intermediate densities correlating with fibrous lesions, though overlap between densities makes distinction between fibrous and soft plaques problematic. 1

Clinical Significance in Asymptomatic Patients

• In asymptomatic individuals with calcium score of zero, non-calcified plaque is present in approximately 6-10% of cases when CCTA is performed. 4, 5, 6

• Among asymptomatic patients with zero calcium score who have non-calcified plaque detected on CCTA, the vast majority (89-94%) have non-obstructive disease, with only 1% having obstructive stenosis. 5, 6

• The prognostic significance of isolated non-calcified plaque in asymptomatic individuals with zero calcium score appears negligible, with no clinical events during median 22-month follow-up in the largest series. 5

Critical Limitations of Calcium Scoring Alone

• Calcium scoring substantially underestimates total plaque burden because it cannot quantify non-calcified plaque, which may represent more vulnerable, rupture-prone lesions. 1

• The American Heart Association notes that spatial resolution of non-contrast CT (750 μm) is insufficient to detect thin fibrous caps (70 μm) that characterize vulnerable plaques. 1

• While some research suggests experienced observers can occasionally identify non-calcified plaque on calcium scoring studies through positive remodeling and hypoattenuation, this has low sensitivity (39%) despite reasonable positive predictive value (88%) and is not part of standard clinical practice. 7

Algorithmic Approach for Asymptomatic Adults

For risk assessment only (no symptoms):

• Calcium scoring is appropriate and sufficient for cardiovascular risk stratification in asymptomatic adults aged 40-75 with intermediate ASCVD risk. 1, 2
• CCTA is not indicated in truly asymptomatic individuals for screening purposes, as the detection of non-calcified plaque in this population has unclear clinical benefit. 1

If non-calcified plaque detection is clinically necessary:

• Proceed directly to CCTA with contrast rather than calcium scoring alone. 1
• CCTA provides comprehensive assessment of total plaque burden (calcified and non-calcified), stenosis severity, and plaque characteristics. 1

Common Pitfalls to Avoid

• Do not assume a zero calcium score excludes coronary atherosclerosis—it only excludes calcified plaque. 2, 3

• Do not order CCTA in patients with extensive coronary calcification (Agatston >400), as severe calcifications lead to overestimation of stenosis severity and poor image quality. 8

• Recognize that calcium scoring provides anatomic information about plaque burden but does not provide functional or physiological assessment of ischemia. 1

• In symptomatic patients with zero calcium score, particularly those under age 40, non-calcified obstructive disease remains possible (present in 7-38% of symptomatic patients) and CCTA should be considered based on pretest probability. 3