The CAC score quantifies calcified plaque in coronary arteries from a non-contrast cardiac CT scan. Calcium accumulates in established atherosclerotic plaque.
Mechanism — Reflects cumulative coronary atherosclerotic burden across a lifetime. Doesn't show soft (vulnerable) plaque — CT angiography or CCTA does. A high CAC = established disease; a zero CAC at age 50+ is reassuring but not absolute.
Use case — Single scan at 40-50 (men) or 45-55 (women) as a personalized risk readout. Scores: 0 = no calcified plaque; 1-100 = mild; 100-400 = moderate; >400 = high risk. Re-scan only when clinically indicated.
Caveats — Radiation exposure is low but non-zero (1-2 mSv). Doesn't show soft plaque or measure plaque growth rate. A zero CAC does not rule out cardiovascular disease — pair with ApoB and lifestyle history.