We used an HCD approach based on the “3I” model of IDEO, which includes 3 phases: inspiration, ideation, and implementation [23,24]. Across the 3 phases, we engaged distinct participant groups and data collection approaches, including provider and staff interviews (phase 1), stakeholder customer discovery interviews (phase 2), and intervention delivery with surveys and qualitative interviews among AYAs and mentors (phase 3). We incorporated the principles of HCD throughout, including engaging stakeholders early and throughout the design process, understanding the needs of patients, clinicians, and staff involved in diabetes care, and taking a systems approach to design [25,26]. We enhanced standard HCD steps with rigorous qualitative and customer discovery methods [27], adapted for implementation science [28], to aid in a rigorous, adopter-centered assessment of the “jobs, pains, and gains” that would be addressed by the transition intervention. Collectively, this iterative process followed best practices for designing for dissemination and sustainability and ensuring strong fit-to-context [29].

In the first phase of the project, we gathered perceptions and ideas from providers and staff involved in delivering specialty diabetes care across 4 University of California medical centers. An open-ended question about transitions from pediatric to adult care was added to a semistructured interview guide for an existing qualitative study examining telehealth use for specialty diabetes care. This study used purposive and snowball sampling to identify adult and pediatric endocrinologists, nurses, and staff involved in specialty diabetes care. Interviews lasted 1 hour, were conducted on Zoom, and were recorded and transcribed. We conducted thematic analysis using line-by-line coding in Dedoose (Sociocultural Research Consultants, LLC) [30], as fully described elsewhere [31]. Responses to the transition question were coded and analyzed separately using qualitative content analysis. The research team organized and discussed the main findings for this question.

The second design phase was customer discovery, a process widely used across industries to identify intervention adopters’ and influencers’ “jobs, pains, and gains” and to develop value propositions tailored to different types of stakeholders (ie, adopters and influencers) involved in the clinical transition workflow [32-34]. Our process, adapted for implementation science, focused on understanding (1) adopters’ and influencers’ perspectives on the most important jobs to be done regarding transitions for patients with T1D, (2) the “pains” (ie, current challenges in supporting transition) and “gains” (ie, opportunities for improved experience or impact) for each group, and (3) how each group defines success [27,28,35]. We first developed a value proposition hypothesis, then conducted customer discovery to validate this hypothesis, and finally established a final value proposition statement. Value proposition statements articulate how the proposed intervention will relieve pains and create gains while carrying out the jobs to be done. Four groups of adopters and influencers were included in customer discovery: (1) people with T1D who had experienced the transition from pediatric to adult care in the past 10 years, (2) pediatric endocrinologists, (3) adult endocrinologists, and (4) diabetes educators. We recruited participants through a snowball sampling strategy, beginning with the participants from the phase 1 qualitative study. Customer discovery interviews were conducted over the telephone and lasted between 15 and 30 minutes; the interview guide was informed by standard customer discovery questions [27]. Questions for people with diabetes included the following: (1) Can you tell me about your experience transitioning from pediatric to adult care? (2) What types of things were you most concerned about? (3) What were the main challenges and how did you deal with them? (4) Is there anything that could have made the transition easier? (5) What would an ideal transition intervention look like? (6) How would you define a successful transition? Questions for providers and staff included the following: (1) What is your role in transitions of care for patients with T1D? (2) Can you walk me through a typical transition? (3) How do you feel your health system/department/division/clinic is doing at transitions? (4) What resources are offered? (5) How do you think transitions could be improved? (6) How important do you think transitions are (for you, your colleagues, your patients, and leadership)? (7) What motivates you to want to improve transitions? Responses were captured in notes during interviews and were summarized immediately afterward.

This study was reviewed and approved by the UC Davis Institutional Review Board (approval number 1982341). Interview participants for phases 1 and 2 provided verbal consent. AYA participants in phase 3 provided written informed consent if aged 18 years or older and written assent along with written informed consent from the parent or guardian if younger. Participants who turned 18 during the study were reconsented.

Qualitative study participants included 5 pediatric endocrinologists, 7 adult endocrinologists, 4 diabetes educators, 2 diabetes pharmacists, and 8 staff members involved in specialty diabetes care. We identified 3 main findings related to transitions from pediatric to adult care for persons with T1D: (1) There is a perception among all types of clinicians and staff that transitions to adult care need improvement; (2) Levels of support for transitions vary widely depending on the patient’s distance from the health system; and (3) Components that may be helpful for a transition program include navigating the health care system independently (eg, insurance, appointments, pharmacy, and device companies) and a transition plan available to all members of the care team (pediatric and adult) in the EHR.

We completed customer discovery interviews with 36 participants, including 16 people with diabetes, 8 pediatric endocrinologists, 6 adult endocrinologists, and 6 diabetes educators. Adults with diabetes who had previously transitioned emphasized that, during that period of their lives, their primary concern was not health outcomes per se but succeeding in broader developmental milestones, such as starting college, entering the workforce, or living independently. They described the transition as most effective when it supported their ability to manage diabetes in a way that enabled these life goals, rather than focusing narrowly on avoiding adverse health events like DKA or hospitalization. When reflecting on what would have helped them most during the transition, participants consistently identified 3 essential components: access to peer support, a space to ask questions without judgment, and the development of strong self-advocacy skills. Table 1 summarizes the motivating gains, pains, and value proposition statements for each adopter or influencer group.

Across interviews with pediatric endocrinologists, adult endocrinologists, and diabetes educators, several key themes emerged about the transition from pediatric to adult diabetes care. Pediatric endocrinologists saw their primary role as initiating transition conversations and referring patients to adult care, often with support from diabetes educators. Many described significant emotional distress when patients failed to transition successfully, especially when long-term patients experienced poor outcomes. They also expressed discomfort about continuing to refill insulin prescriptions for patients who should have moved on, and they described time and resource limitations as ongoing challenges. Adult endocrinologists focused more on ensuring that young adults received the care and tools they needed to manage diabetes in adulthood. While they reported less emotional strain, given they typically meet patients after the transition, they highlighted high no-show rates and limited background information as key pain points. Diabetes educators emphasized their role in providing resources and answering questions about what to expect in adult care but noted that strict oversight of how they use their time limited their ability to support transitions more fully. They were enthusiastic about anything that could reduce the burden of 1:1 education and help more patients. Customer discovery significantly influenced the intervention design, including prompting the addition of “T1D mentors,” adults who have transitioned in the past 10 years, to share their experiences and strategies, and having a specific focus on advocating for oneself (eg, explaining diabetes to others, asking for accommodations, etc). These features created the “gains” sought by participants in terms of connecting with other people with T1D and improving confidence, and addressed the “pains” of anxiety around self-advocacy.

We identified 73 eligible patients at the beginning of the study. Of these, 25 were enrolled through in-clinic recruitment and EHR messaging. Seven eligible participants declined, citing that they were either not interested in research (n=4), had a work conflict (n=1), were concerned about the time commitment (n=1), or did not feel comfortable participating in English (n=1). The remaining 41 did not respond to StudyPages (Yuzu Labs PBC) messages and were not seen in the clinic during the recruitment window. Table 2 shows the demographic and health characteristics of participants for phase 3 testing. The group was diverse, with 48% (12/25) female participants, 40% (10/25) of Hispanic or Latino ethnicity, and a variety of self-identified races. The median age of participants was 18 (IQR 18-19), and median number of years living with diabetes was 6 (IQR 4-12.5). Self-reported employment status varied, with 44% (11/25) enrolled as students (including 3/25, 12% with part-time jobs), 12% (3/25) working part-time, 4% (1/25) working full-time, and 20% (5/25) unemployed and not in school.

The intervention for the first cohort consisted of three 75-minute sessions scheduled monthly. In the first cohort, 7 out of 9 participants enrolled attended the first session, but only 3 participants attended the subsequent 2 sessions, and only 2 participants completed all 3 sessions. We subsequently adapted the intervention to 2 sessions delivered over consecutive weeks in response to feedback from cohort 1 participants. In the second cohort, 5 out of 8 participants enrolled attended session 1, and 4 also attended session 2. In the third cohort, only 2 out of 8 participants enrolled attended the first session, and only 1 attended both sessions. Attendance appeared to be influenced in part by the timing of the sessions relative to enrollment, with lower participation observed when there was a longer delay between enrollment and the session start.

After the completion of cohort 1, we also increased the use of the chat function in subsequent sessions, as many participants were uncomfortable speaking on video but actively participated in the chat when asked to do so. We also adapted the transition plan component of the intervention; rather than asking participants to fill out and share their transition plans, participants preferred to watch one of the T1D mentors fill out the transition plan template and discuss the rationale behind their choices. Table 3 shows the resulting core components and adaptive forms of the intervention.

We completed a total of 15 qualitative interviews (9 participants, 5 T1D mentors, and 1 facilitator) during phase 3. Table 4 summarizes qualitative findings and provides illustrative quotes. Participants described the intervention as helpful, prompting them to think about aspects of managing their care they had not previously considered, and improving their confidence that they would transition successfully to adult care. The 2 components highlighted by participants as being most valuable were the T1D mentors and peer support. Many participants had not previously spoken with other people with T1D and appreciated the open discussions about challenges others had encountered and how they overcame them. These findings suggest that the core needs identified during customer discovery, particularly peer support, judgment-free discussion, and self-advocacy, were reflected in participants’ experiences of the intervention. T1D mentors and facilitators also perceived the intervention to be valuable. Mentors and participants had different perspectives on session participation. While mentors were concerned that some participants were not engaged in the sessions, participants themselves noted that, although they may have had their cameras turned off or not spoken often, they were nonetheless engaged and learned from the discussions between the peer mentors and other participants. Qualitative interviews also provided insights into the intervention timing, ideal number of participants, and perspectives on topics and exercises.

Seven facilitators and mentors (100% response rate) completed the intervention appropriateness measure and feasibility of intervention measure surveys. They rated the intervention as having good feasibility (mean 4.25, SD 0.52) and appropriateness (mean 4.43, SD 0.53). Of the 14 AYAs who participated in the sessions, only 3 completed the acceptability of intervention measure survey. These 3 participants rated the intervention as having high acceptability (mean 4.67, SD 0.29).