Using Multistate Models and Qualitative Interviews to Comprehensively Characterize Substance Use Disorder Care Transitions in a US Health Care System: Protocol for a Mixed-Methods Study.

Background: Many substance use disorder (SUD) care pathways exist in health care systems. However, patients with SUD often report poor care experiences, particularly regarding timely follow-up, clinician and general satisfaction ratings, and care communication. As SUD care pathways involve transitions across clinicians and venues of care, adequate treatment requires coordination across clinicians and settings to ensure unmet needs are addressed, and appropriate SUD care is delivered. Surprisingly little is known about the real-world care pathways patients engage in once identified as having SUD. Objective: This study protocol describes research that will comprehensively characterize the pathways of care used by those who obtain care for SUD and compare the quality and outcomes associated with these care pathways. Specific aims are to (1) apply multistate models (MSM) to characterize the spectrum of care transitions among patients with SUD within a large integrated health system, (2) generate data-driven insights to improve care delivery for SUD using estimated MSMs, and (3) observe and explore patient and clinician experiences with care transitions across common care pathways using qualitative methods. Methods: Quantitative data sources will include electronic health care records, insurance claims, self-reported measures of substance use and SUD symptoms, and death data from an integrated health care system in Washington State. To identify care pathways, we will apply continuous time, multistate modeling methods to empirically observe the longitudinal course of SUD care transitions undertaken by patients over time; each "state" or occurrence of care will be characterized by the intervention received (eg, evaluation or assessment, behavioral treatment or counseling, and pharmacotherapy) and setting of care (eg, outpatient, intensive outpatient, or inpatient or residential). The estimated parameters from the fitted MSMs will be transformed or interpreted to characterize SUD care quality, such as wait times for SUD visits, and receiving an adequate psychotherapy dose. To compare outcomes associated with care pathways, we will examine terminal states, including death and loss to follow-up. Using a mixed methods design, we will sample and interview patients engaged in empirically derived pathways to understand their care experiences, observe and interview clinicians to elucidate health system factors that impact SUD care transitions, and integrate qualitative and quantitative findings using joint displays. Results: This study was funded in June 2025 and received institutional review board approval on July 17, 2025. We expect preliminary data collection for quantitative analyses to be complete by May 2026, and final data collection will be complete by November 2027. We expect qualitative data collection completion by November 2029. Conclusions: This exploratory study will identify and compare the quality and outcomes associated with common pathways that patients take when they obtain treatment for SUD and provide decision-makers with information on how to better organize SUD care delivery.