Higher coronary artery calcium (CAC) identifies individuals at increased atherosclerotic cardiovascular disease (ASCVD) risk. Whether it can also identify individuals likely to derive net benefit from aspirin therapy is unclear.

To examine the association between CAC, bleeding, and ASCVD and explore the net estimated effect of aspirin at different CAC thresholds.

Prospective population-based cohort study of Dallas Heart Study participants, free from ASCVD and not taking aspirin at baseline. Data were analyzed between February 1, 2020, and July 15, 2020.

Coronary artery calcium score in the following categories: 0, 1-99, and 100 or higher.

Major bleeding and ASCVD events were identified from International Statistical Classification of Diseases and Related Health Problems, Ninth Revision codes. Meta-analysis-derived aspirin effect estimates were applied to observed ASCVD and bleeding rates to model the net effect of aspirin at different CAC thresholds.

A total of 2191 participants (mean [SD], age 44 [9.1] years, 1247 women [57%], and 1039 black individuals [47%]) had 116 major bleeding and 123 ASCVD events over a median follow-up of 12.2 years. Higher CAC categories (CAC 1-99 and ≥100 vs CAC 0) were associated with both ASCVD and bleeding events (hazard ratio [HR], 1.6; 95% CI, 1.1-2.4; HR, 2.6; 95% CI, 1.5-4.3; HR, 4.8; 95% CI, 2.8-8.2; P < .001; HR, 5.3; 95% CI, 3.6-7.9; P < .001), but the association between CAC and bleeding was attenuated after multivariable adjustment. Applying meta-analysis estimates, irrespective of CAC, aspirin use was estimated to result in net harm in individuals at low (<5%) and intermediate (5%-20%) 10-year ASCVD risk and net benefit in those at high (≥20%) ASCVD risk. Among individuals at lower bleeding risk, a CAC score of at least 100 identified individuals who would experience net benefit, but only in those at borderline or higher (≥5%) 10-year ASCVD risk. In individuals at higher bleeding risk, there would be net harm from aspirin irrespective of CAC and ASCVD risk.

Higher CAC is associated with both ASCVD and bleeding events, with a stronger association with ASCVD. A high CAC score identifies individuals estimated to derive net benefit from primary prevention aspirin therapy from those who would not, but only in the setting of lower bleeding risk and estimated ASCVD risk that is not low.