A national digital recruitment campaign for the Phase 3 LIBREXIA-AF atrial fibrillation trial spent $163,949 across 82.7 million ad impressions to enroll 1,406 online registrants. Despite broad geographic reach across 260 U.S. metro areas, minority representation was strikingly thin: every $100,000 in advertising yielded 334 women, but only 36 African American and 27 Latino recruits. Community income level showed no meaningful association with minority recruitment yield, undermining the hypothesis that digital outreach would naturally overcome socioeconomic barriers to trial participation.
The findings arrive at a moment when the FDA and NIH are intensifying pressure on sponsors to diversify cardiovascular trial cohorts — a reasonable demand given that atrial fibrillation prevalence, stroke risk, and anticoagulation outcomes differ meaningfully across ethnic groups. The LIBREXIA-AF trial tests a novel factor XIa inhibitor, making representative data particularly consequential for real-world prescribing. These results suggest that digital advertising — even at national scale — functions more as a convenience amplifier for already-engaged populations than as a genuine diversity tool. The 4.5% African American enrollment rate falls far below the roughly 13% U.S. population share.
Limitations are significant: this is a feasibility and cost analysis, not an outcomes study. Causality cannot be established, and cultural, linguistic, and trust-based barriers to enrollment are unquantified. As a preprint posted on medRxiv and not yet peer-reviewed, these cost estimates and conclusions may be revised. The editorial assessment: confirmatory of a known problem, but valuable for its precise cost-per-recruit benchmarking.