CT Coronary Calcium Scoring (CAC Score): A Practical, Evidence-Based Guide for Clinicians

CT Coronary Calcium Scoring (CAC Score): A Practical, Evidence-Based Guide for Clinicians

Introduction

CT coronary calcium scoring is a non-invasive, rapid, and widely validated tool for quantifying coronary atherosclerotic burden. By detecting and measuring calcified plaque in the coronary arteries, the CAC score refines cardiovascular risk assessment beyond traditional risk factors and directly influences preventive cardiology decisions—especially statin initiation and intensity.

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What Is CT Coronary Calcium Scoring?

Coronary calcium scoring uses non-contrast, ECG-gated cardiac CT to detect calcified atherosclerotic plaques in the coronary arteries. The amount of calcium is quantified as an Agatston score, which correlates strongly with total plaque burden and future atherosclerotic cardiovascular disease (ASCVD) events.

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How the Test Is Performed

Scan type: Non-contrast, ECG-gated CT

Scan time: ~5–10 minutes

Radiation dose: Low (≈1 mSv or less with modern scanners)

Preparation: No fasting; beta-blockers usually not required

Contrast: Not used

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The Agatston Score: Interpretation

CAC Score Interpretation Clinical Meaning

0 No detectable calcium Very low short-term risk

1–99 Mild calcification Early atherosclerosis

100–299 Moderate calcification Definite CAD

≥300 Severe calcification High ASCVD risk

Percentile-based interpretation (age, sex, ethnicity) further refines risk, particularly in younger patients.

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Clinical Indications (Most Useful Scenarios)

✅ Primary Prevention (Key Role)

Adults 40–75 years

Borderline or intermediate ASCVD risk (5–20%)

Uncertainty about starting statins

✅ Risk Reclassification

Strong family history of premature CAD

Metabolic syndrome

Chronic inflammatory conditions

Patients reluctant to start lifelong statin therapy

❌ Not Routinely Indicated In

Known CAD or prior MI/PCI/CABG

Symptomatic patients (use CCTA or stress testing)

Very low-risk young adults

Advanced CKD (interpret cautiously)

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CAC Score and Statin Decision-Making

Guideline-based approach (ACC/AHA):

CAC = 0

→ Consider deferring statin (except in diabetes, smokers, strong FHx)

CAC 1–99

→ Statin favored (especially age >55)

CAC ≥100 or ≥75th percentile

→ Statin therapy clearly indicated

Higher CAC = higher statin intensity consideration

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Prognostic Value: Why CAC Matters

CAC is one of the strongest predictors of future coronary events

Outperforms traditional risk factors alone

Provides “warranty period”:

CAC 0 → ~5–10 years of very low event rates

Predicts:

MI

Cardiovascular mortality

All-cause mortality

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CAC vs Other Cardiac Tests

Test What It Detects Best Use

CAC Score Calcified plaque burden Risk stratification

CCTA Lumen + soft plaque Symptomatic patients

Stress Test Ischemia Functional assessment

Carotid IMT Arterial thickness Limited predictive value

Key Point: CAC does not assess stenosis or ischemia.

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Special Clinical Situations

Diabetes Mellitus

CAC refines risk even in diabetics

CAC = 0 identifies a lower-risk subgroup

Young Patients (<45 years)

Any CAC is abnormal

Suggests premature atherosclerosis

Women

CAC improves risk prediction where traditional scores may underestimate risk

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Limitations of Calcium Scoring

Does not detect non-calcified (soft) plaques

Zero score ≠ zero lifetime risk

Cannot assess lesion severity or ischemia

Incidental extracardiac findings may occur

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Follow-Up and Repeat Scanning

CAC = 0: Repeat in 5 years (earlier if risk factors worsen)

CAC >0: Repeat usually not required; focus on aggressive risk modification

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Practical Take-Home Points

CAC score is a powerful, cost-effective preventive cardiology tool

Best used in borderline–intermediate risk adults

Strongly guides statin decisions

CAC = 0 provides reassurance; CAC ≥100 mandates action

Complements—but does not replace—clinical judgment

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Summary

CT coronary calcium scoring bridges the gap between population-based risk calculators and individual patient risk. Its ability to visualize subclinical atherosclerosis makes it one of the most impactful investigations in modern preventive cardiology. When used appropriately, CAC scoring improves patient adherence, personalizes therapy, and ultimately reduces cardiovascular events.