Enrollment represents the transition from candidate to participant, the formal point at which an individual who has completed screening, met all eligibility criteria, and provided informed consent becomes an active subject in the clinical trial. This milestone triggers regulatory counting for enrollment targets and initiates the participant's involvement in study procedures. The enrollment process must be executed precisely, with clear documentation demonstrating that all prerequisites were satisfied before enrollment occurred.

The sequence of enrollment activities is critical for regulatory compliance. Informed consent must be obtained before any screening procedures are performed, and eligibility must be confirmed before randomization or treatment assignment. Documentation must demonstrate that consent preceded screening, that all required screening assessments were completed, that each eligibility criterion was evaluated and met, and that the enrollment date reflects when all requirements were satisfied. Any deviation from this sequence may constitute a protocol violation with potential implications for data integrity.

Enrollment metrics drive critical operational decisions throughout trial conduct. Sponsors track enrollment against projections to identify sites falling behind expectations and assess whether overall timelines are achievable. Enrollment curve analysis reveals whether recruitment activities are producing desired results and whether adjustments are needed. Competitive enrollment information indicates how the study compares to similar trials in the therapeutic area. These metrics inform decisions about adding sites, extending enrollment periods, or implementing additional recruitment strategies.