Process evaluation protocol for the D1 Now cluster randomised controlled trial to improve outcomes for young adults with type 1 diabetes

<ns3:p>Background Young adults with type 1 diabetes often experience suboptimal outcomes compared to other age groups. D1 Now is a multi-component intervention (Agenda-Setting Tool; Support Worker) developed with a Young Adult Panel to improve engagement and self-management. Following a pilot trial, the definitive cluster randomised controlled trial (RCT) is planned across multiple Irish clinics. This process evaluation is designed to explore implementation and delivery of the D1 Now intervention, as well as trial processes. Methods The process evaluation will run in parallel with the definitive D1 Now cluster RCT in 12 hospital diabetes clinics across Ireland between 2026–2027. Data collection will focus on four domains: (1) implementation (fidelity, reach, adaptations), (2) mechanisms of impact (testing the pathways specified in the programme theory), (3) context (clinic, team, and system-level influences), and (4) acceptability and feasibility (young adult and staff perceptions). All trial participants will contribute routine quantitative process data. Quantitative data sources include recruitment logs, fidelity checklists, clinic attendance, and a mechanisms of impact questionnaire administered at baseline and 12 months. Quantitative data will be summarised descriptively. Qualitative data will be collected through online semi-structured interviews with a purposive subsample of young adults, support workers, and clinic staff from both intervention and control sites after 12-month follow-up and analysed thematically. Quantitative and qualitative findings will be integrated through triangulation. Discussion This process evaluation will provide crucial insights into the delivery, reception, and contextual influences of the D1 Now intervention. The involvement of the D1 Now Young Adult Panel throughout the evaluation strengthens the validity and relevance of findings. Results will support the interpretation of trial outcomes and provide practical guidance for optimisation, sustainability, and scale-up, or adaptation if outcomes are mixed. Registration ISRCTN28944606</ns3:p>