Coronary Artery Calcium (Agatston)
Interpretation of the total Agatston coronary artery calcium score for cardiovascular risk stratification (MESA framework).
The Agatston coronary artery calcium (CAC) score quantifies calcified atherosclerotic plaque on non-contrast ECG-gated (or, increasingly, non-gated) chest CT and is one of the strongest independent predictors of future cardiovascular events.
📐 Formula
Agatston score = Σ (plaque area × density-weighted factor), summed over all coronary lesions
🎯 When to Use
- Refining ASCVD risk in asymptomatic intermediate-risk adults to guide statin therapy.
- Reporting incidentally visible coronary calcification on any chest CT.
- Reclassifying borderline patients where treatment decisions are uncertain.
⚙️ How It Works
- Each calcified lesion (≥ 130 HU, area ≥ 1 mm²) is scored by its area multiplied by a factor of 1–4 based on peak density.
- Lesion scores are summed across the left main, LAD, circumflex and right coronary arteries to give the total Agatston score.
- The total is compared with population distributions (e.g. MESA) matched for age, sex and ethnicity to derive a percentile.
📊 Interpreting the Result
- Score 0 — no identifiable calcified plaque; very low 10-year event risk and negative reclassification (statin often deferrable).
- Score 1–99 — mild calcification; modest risk increase.
- Score 100–399 — moderate calcification; substantially elevated risk, statin generally favoured.
- Score ≥ 400 — extensive calcification; high cardiovascular risk, aggressive risk-factor modification indicated.
- A score above the 75th percentile for age/sex/ethnicity (MESA) denotes higher-than-expected burden regardless of absolute value.
⚠️ Limitations & Pitfalls
- Detects only calcified plaque; non-calcified (soft) plaque may cause events with a score of 0, particularly in younger patients and smokers.
- Not a diagnostic test for obstructive stenosis and not indicated in symptomatic patients needing acute evaluation.
- Scores from non-gated or low-dose scans are less reproducible than dedicated gated acquisitions.
📚 References
- Agatston AS, et al. Quantification of coronary artery calcium using ultrafast computed tomography. J Am Coll Cardiol. 1990;15:827–832.
- Detrano R, et al. (MESA). Coronary calcium as a predictor of coronary events in four racial or ethnic groups. N Engl J Med. 2008;358:1336–1345.
- Hecht H, et al. SCCT/STR guidelines for coronary artery calcium scoring. J Cardiovasc Comput Tomogr. 2017;11:74–84.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.