AIMS: To assess the impact of sampling bias due to reported as well as unreported exclusion of the target population in a multi-center randomized controlled trial (RCT) of ST-elevation myocardial infarction (STEMI).

METHODS AND RESULTS: We compared clinical characteristics and mortality between participants in the DANAMI-3 trial to contemporary non-participants with STEMI using unselected registries. A total of 179 DANAMI-3 participants (8%) and 617 contemporary non-participants (22%) had died (Log-Rank: P < 0.001) after a median follow-up of 1333 days (range: 1-2021 days). In an unadjusted Cox regression model all groups of non-participants had a higher hazard ratio to predict mortality compared to participants: eligible excluded (n = 144) (hazard ratio: 3.41 (95% CI: (2.69-4.32)), ineligible excluded (n = 472) (hazard ratio: 3.42 (95% CI: (2.44-4.80), eligible non-screened (n = 154) (hazard ratio: 3.37 (95% CI: (2.36-4.82)), ineligible non-screened (n = 154) (hazard ratio: 6.48 (95% CI: (4.77-8.80).

CONCLUSION: Sampling bias had occurred due to both reported and unreported exclusion of eligible patients and the difference in mortality between participants and non-participants could not be explained only by the trial exclusion criteria. Thus, screening logs may not be suited to address the risks of sampling bias.