People with severe mental illness have a substantially increased risk of undiagnosed and insufficiently treated somatic disease. Somatic Screening in the Capital Region Mental Health Service in Denmark (SomaScreen) is a service-level intervention implemented in psychiatric outpatient clinics in the Capital Region of Denmark to improve the detection and follow-up of somatic disease among patients with psychotic and affective disorders.

This study evaluates whether integrating structured somatic screening into mental health services leads to improved identification and management of somatic disease compared with care as usual. Using a quasi-experimental controlled design with a matched cohort, outcomes among patients exposed to the SomaScreen intervention are compared with those of patients receiving usual care in comparable psychiatric outpatient clinics outside the Capital Region.

Background and Rationale

Individuals with severe mental illness experience pronounced health inequalities, including a markedly elevated risk of somatic disease and premature mortality. A substantial proportion of this excess mortality is attributable to common physical conditions such as cardiovascular disease, respiratory disease, diabetes, and cancer. These conditions are often underdiagnosed or insufficiently managed in this population due to complex interactions between illness-related factors, treatment side effects, socioeconomic vulnerability, and barriers in accessing somatic health care.

In Denmark, most diagnosis and treatment of somatic disease occurs in general practice, either directly or through referral to secondary care. However, patients with severe mental illness may face difficulties engaging with general practice, and coordination across sectors remains challenging. Strengthening somatic disease detection and care pathways within psychiatric services may therefore represent an important opportunity to reduce health inequalities.

The SomaScreen Intervention

Somatic Screening in the Capital Region Mental Health Service in Denmark (SomaScreen) was implemented in psychiatric outpatient clinics in the Capital Region of Denmark as a service-level initiative to improve early detection and management of somatic disease. The intervention integrates structured somatic screening into psychiatric outpatient care and actively supports transitions to general practice.

Somatic examinations are conducted by specially trained somatic nurses and general practitioner consultants embedded within psychiatric outpatient clinics. A standardized consultation model is used, incorporating systematic preparation, extended consultation time, and a structured questioning approach tailored to patients with severe mental illness. When somatic disease is suspected or identified, referral to general practice is facilitated, including support with appointment booking and follow-up.

The intervention is delivered within Flexible Assertive Community Treatment (F-ACT) and OPUS outpatient clinics, both of which are multidisciplinary mental health service models for patients with severe mental illness. OPUS primarily serves young adults with early psychosis, whereas F-ACT serves a broader population with severe mental disorders across age groups. Both models emphasize continuity of care, assertive outreach, and treatment within patients' everyday environments.

Recruitment and Inclusion Criteria

Eligible participants are adult patients (18+) referred to F-ACT or OPUS outpatient clinics who are starting a new outpatient treatment episode. Patients must have a primary diagnosis of psychotic or affective disorder (F20-39) and may have comorbid substance use disorders (F10-19). Geriatric outpatient clinics are not included, and patients may be of any adult age. Patients who meet these criteria are systematically offered somatic screening.

Study Design

Because SomaScreen was implemented as a routine service initiative prior to the establishment of a research protocol, the intervention was not designed as a randomized clinical trial. Allocation to the intervention was determined by service delivery, and randomization was not feasible. Patients receiving SomaScreen therefore constitute a cohort defined by exposure to the intervention rather than an experimental arm.

To enable evaluation of intervention effects, the study uses a quasi-experimental controlled design with a matched cohort. Patients exposed to SomaScreen are compared with a control cohort receiving care as usual in comparable psychiatric outpatient clinics located in other major urban regions of Denmark. Matching is conducted to enhance comparability and reduce confounding.

Blinding is not applied in this study, as identification of intervention exposure is required for cohort construction and matching procedures. Participants in both the intervention and control cohorts are followed for up to two years from the start of the outpatient treatment episode, allowing longitudinal assessment of outcomes.

Intervention Cohort Operationalization

There is a single intervention cohort comprising all patients meeting inclusion criteria and starting a new outpatient treatment episode in SomaScreen-implementing FACT/OPUS clinics. Two complementary analysis approaches will be applied to this cohort:

Intention-to-treat analysis (primary): Includes all patients in the intervention cohort, regardless of actual participation in SomaScreen. This approach reflects real-world effectiveness under routine service conditions.

Adherence-stratified analysis (supplementary): Applied to patients captured in intervention-specific data collection (i.e., those who attended at least the initial somatic nurse screening). Patients will be stratified by adherence level to examine dose-response effects, with higher exposure values assigned to those completing additional intervention steps (screening completion, GP appointment booking, and GP consultation attendance).

Evaluation Framework

The evaluation comprises three complementary components: effectiveness, process, and health economic evaluation.

The effectiveness evaluation examines whether exposure to SomaScreen is associated with improved identification and management of somatic disease compared with care as usual. The process evaluation investigates whether the intended mechanisms of action occur in practice, for whom the intervention works best, and how the screening and referral components function within routine clinical settings. The health economic evaluation assesses whether the intervention represents a cost-effective use of health care resources.

Data Sources and Analysis Overview

The study combines intervention-specific data with nationwide Danish register data, linked at the individual level through secure, pseudonymized procedures. Register-based data enable longitudinal follow-up and comprehensive assessment of health care utilization and outcomes across sectors.

Analyses are conducted using appropriate regression-based methods for matched cohort data and clustered observations.

Inclusion Criteria:

• Patients aged 18 years or older.
• Referred to FACT or OPUS psychiatric outpatient clinics in the Capital Region of Denmark.
• Starting a new outpatient treatment episode in FACT or OPUS.
• Diagnosed with psychotic or affective disorders (ICD-10 F20-F39), including those with comorbid substance use disorders (F10-F19).

Exclusion Criteria:

• Individuals younger than 18 years.
• Patients in geriatric outpatient clinics.
• Individuals not in the target diagnosis group (i.e., without psychotic or affective disorders, F20-F39).
• Individuals who do not meet the inclusion criteria above.

Individual participant data will not be shared, in accordance with Danish data protection regulations. Data contain sensitive health information from psychiatric patients and cannot be shared outside the research team.