CT coronary calcium scoring

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CT Coronary Calcium Scoring (CAC)

What It Is

CT coronary calcium scoring (also called coronary artery calcification scoring, CAC) is the simplest application of cardiac CT and does not require iodinated contrast. It acquires non-contrast axial images through the heart to detect and quantify calcified deposits within the coronary artery walls. Calcium on CT appears as dense, bright-white structures even without contrast - because hydroxyapatite (the main crystal in atherosclerotic calcification) has high x-ray attenuation. The procedure delivers a very low radiation dose (~1-2 mSv). - Harrison's Principles of Internal Medicine 22E, p. 1923

Non-contrast CT axial slices showing coronary calcium scoring - Panel A shows extensive calcification in the proximal LAD (arrow), Panel B shows proximal spotty calcification of the RCA (arrow). This patient's Agatston score was 457.

Non-contrast cardiac CT for coronary calcium scoring. A: Proximal LAD with extensive calcification (arrow). B: Proximal RCA with spotty calcification (arrow). Agatston score = 457, placing this patient in a higher risk group regardless of Framingham risk score. - Goldman-Cecil Medicine

The Agatston Score - How It's Calculated

The Agatston score is the standard quantification method. For each calcified lesion:

The area of each calcified focus (pixels >130 Hounsfield units) is measured
Multiplied by a density factor based on the peak CT attenuation of that lesion
All lesions across the entire coronary tree are summed to give the total score

Volume scores and mass scores are less commonly used alternatives. Reference data stratified by age and sex are available, allowing the score to be reported as a percentile. - Grainger & Allison's Diagnostic Radiology; Goldman-Cecil Medicine

Score Categorization

Agatston Score	Category	Interpretation
0	No calcification	No detectable plaque; excellent prognosis
1-10	Minimal	Very small calcium burden
10-100	Mild	Mild atherosclerosis
100-400	Moderate	Moderate atherosclerotic burden
>400	Severe	Extensive calcification

- Harrison's Principles of Internal Medicine 22E, p. 1923

What CAC Score Measures - and What It Does NOT

Measures: Overall atherosclerotic plaque burden in the coronary arteries
Does NOT correlate with the physiologic or anatomic significance of any individual stenosis - a high calcium score does not mean there is flow-limiting disease
In young symptomatic patients, a negative (zero) calcium score does NOT exclude significant coronary artery stenoses (non-calcified plaques can still cause obstructive CAD)
In high CAC score settings (>400), CT angiography specificity drops because the blooming artifact of calcium obscures luminal evaluation

- Goldman-Cecil Medicine; Grainger & Allison's Diagnostic Radiology

Clinical Indications and Appropriate Use

CAC scoring is most useful for intermediate-risk patients - those with a 10-year Framingham/Pooled Cohort risk of 10-20% - where the result can meaningfully shift management:

Upgrade risk (score high for age/sex) -> intensify preventive therapy, consider statins
Downgrade risk (score unexpectedly low or zero) -> avoid unnecessary statin therapy, reassure

For low-risk patients, a CAC rarely changes management. For already high-risk patients, the result also rarely changes the clinical approach (statins and risk reduction are already indicated). Per the 2010 ACC Appropriate Use Criteria, CAC scoring is appropriate in:

Asymptomatic patients without known CAD who have a family history of premature ischemic heart disease
Asymptomatic intermediate-risk patients for risk stratification

- Grainger & Allison's Diagnostic Radiology; Goldman-Cecil Medicine

Prognostic Power

The prognostic value of CAC is well established:

CAC = 0: 12-year ASCVD event rate well below the 7.5% threshold used for statin recommendations; associated with excellent long-term prognosis
CAC > 100 Agatston units: Relative hazard for coronary events 7-10 fold higher than individuals with no calcification, even after adjustment for all major established risk factors
15-year all-cause mortality in asymptomatic patients ranges from ~3% (CAC = 0) to ~28% (CAC > 1000)
CAC scoring is the most effective and reliable means for reclassifying risk after standard risk factor assessment - it correctly reclassifies both lower-risk individuals who will have events and higher-risk individuals who will not

- Goldman-Cecil Medicine; Harrison's 22E

Sex Differences

From the CAC Consortium (Fuster/Hurst data):

Prevalence of detectable CAC in women ranges from 26% to 72% for ages 50-70
Women with multivessel CAC have nearly 2-fold higher long-term ASCVD mortality than men with equivalent multivessel CAC, possibly because calcium burden layered onto smaller epicardial vessels disproportionately worsens risk in women
CAC scoring is particularly helpful in women, where global risk scores (e.g., Pooled Cohort Equations) can be imprecise

- Fuster and Hurst's The Heart, 15th Ed., p. 2252

Key Technical Notes

Performed without contrast; ECG-gated to minimize cardiac motion
Radiation dose: ~1-2 mSv (very low)
Modern CT equipment with iterative reconstruction can now perform diagnostic CT angiography even in patients with very high CAC scores (previously >400-1000 was considered a contraindication to CTA) - Grainger & Allison's
CAC score is age, sex, and race dependent - always interpret using population-specific percentiles

Recent Evidence Update

A 2025 meta-analysis (PMID 39243235) in JACC Cardiovascular Imaging examined coronary artery calcium density (not just volume/area) and found that calcium density independently predicts cardiovascular events, adding nuance beyond the standard Agatston score - higher density calcium may actually confer lower risk per unit of calcium area, suggesting plaque stability differences.

Summary: CAC scoring is a fast, low-radiation, non-contrast CT tool that quantifies coronary atherosclerosis via the Agatston score. A score of 0 carries excellent prognosis. Its greatest clinical value lies in risk reclassification of intermediate-risk asymptomatic patients to guide statin and preventive therapy decisions. It does not localize stenoses or assess physiology - that requires coronary CTA or stress testing.

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