Coronary Artery Calcium (CAC) Score

What it is

A low-radiation (~1 mSv) ungated CT scan of the chest that quantifies calcium in the coronary arteries. The result is the Agatston score — the sum of calcified plaque area weighted by density — reported in “Agatston units”.

Interpretation

• CAC = 0: very low 10-year cardiovascular event risk; powerful negative predictor in middle-aged adults.
• 1–100: mild plaque, elevated risk — consider statin and risk-factor optimisation.
• 101–400: moderate plaque; established cardiovascular disease for treatment purposes.
• >400: severe; high event risk; aggressive secondary-prevention approach.

Compared to age/sex peers (percentile) is also informative.

When to use it

• Middle-aged adults (~40–75) with intermediate risk by traditional calculators where management decision is uncertain.
• Family history of premature ASCVD.
• High Lp(a) or ApoB.

Not useful in adults already on guideline-recommended therapy for established disease (won’t change management).

Caveats

• Measures calcified plaque only. Younger adults can have substantial soft (uncalcified) plaque with CAC=0.
• A CT angiogram is the more sensitive (and higher-radiation, contrast-using) alternative.

Related entries

ApoB, Cardiovascular disease, Statins.