Elevated lipoprotein(a) (Lp[a]) and apolipoprotein B (apoB) are individually associated with the risk of atherosclerotic cardiovascular disease (ASCVD). Moreover, previous basic research has implicated the potential interaction between apoB and Lp(a) in the atherogenic process. We aimed to determine whether apoB levels significantly modulate ASCVD risk associated with Lp(a) in a large community-based population without baseline cardiovascular disease.

Plasma Lp(a) and apoB were measured in the Atherosclerosis Risk in Communities (ARIC) study. Elevated Lp(a) was defined as the highest race-specific quintile, and elevated apoB was defined as ≥89 mg/dl (median value). The modifying effect of apoB on the Lp(a)-related risk of ASCVD and coronary heart disease (CHD) was determined using Cox regression models adjusted for cardiovascular risk factors.

Among 12,988 ARIC participants, 3,888 ASCVD events and 1754 CHD events were observed. Elevated apoB (≥89 mg/dl) and elevated Lp(a) (race-specific quintile 5) were independently associated with ASCVD (hazard ratio [HR]: 1.19; 95% CI: 1.08-1.30; P <0.001; HR: 1.27; 95% CI: 1.16-1.40; P < .001, respectively). Lp(a)-by-apoB interaction was noted [Lp(a) (quintile 1-4 or quintile 5) * apoB (<89 or ≥89 mg/dl) = 0.002]. Compared to the concordantly low Lp(a) group, the individuals with high Lp(a) had a greater ASCVD risk only when apoB was elevated (HR: 1.48; 95% CI: 1.34-1.63; P < .001).

In the context of primary prevention, ASCVD risk associated with Lp(a) was observed only when apoB was elevated. The measurement of apoB can further refine and contextualize the ASCVD risk associated with Lp(a).