Proactive consultation-liaison-services (CL): comparing PHQ-4 screening with traditional referral pathways in medical inpatients – a prospective comparative pilot study

Background Psychiatric comorbidities are highly prevalent among general hospital inpatients but often remain undetected when mental health referrals rely solely on clinical judgment. Systematic screening may improve identification, yet comparative evidence using structured diagnostic interviews remains limited. The study evaluates diagnostic confirmation rate of systematic PHQ-4 screening versus clinician-initiated referral in identifying psychiatric comorbidities among medical inpatients. Methods In this quasi-experimental pilot study, systematic screening using the Patient Health Questionnaire-4 (PHQ-4) was implemented on one medical ward ( n = 127 admissions), while two comparable wards followed treatment as usual (TAU; n = 267 admissions), with psychosomatic consultations initiated by medical staff based on clinical judgment. Patients screening positive (PHQ-4 ≥ 6 or subscale ≥ 4) were referred for consultation. All referred patients underwent structured diagnostic assessment using the Mini-DIPS interview. Primary outcomes were the proportion of referred patients with a confirmed psychiatric diagnosis (diagnostic confirmation rate) and overall identification rates. Secondary outcomes included time from admission to referral and consultation, as well as treatment recommendations and their uptake. Results Among interviewed patients, screening was associated with a numerically higher rate of diagnostic confirmation than TAU (11/13, 84.6% vs. 8/14, 57.1%), although this difference did not reach statistical significance. A higher proportion of admissions with confirmed psychiatric disorders was observed in the screening group (11/127, 8.7%) compared with TAU (8/267, 3.0%). Referral rates were higher in the screening group (21/127, 16.5% vs. 22/267, 8.2%), and time to consultation was shorter (median 1 vs. 3.5 days). Depressive and anxiety disorders predominated. Follow-up consultation showed high adherence, whereas uptake of inpatient treatment was low. Conclusions Systematic PHQ-4 screening was associated with higher detection of psychiatric comorbidities and earlier consultation-liaison involvement, suggesting that clinician-initiated referral alone may miss substantial psychiatric morbidity. However, given the quasi-experimental design and limited sample size, the findings should be interpreted cautiously. Larger randomized studies are needed to evaluate implementation and patient outcomes.