Effect of depression screening on future depressive symptoms in a persistent pain population: mediation analysis

Introduction: Clinical guidelines for persistent pain recommend screening for psychosocial factors. However, little is known about whether completing a structured depression questionnaire within a clinical encounter is associated with subsequent depressive symptom trajectories. Objective: To evaluate whether exposure to such a questionnaire is associated with depressive symptoms at 6-month follow-up, and, if so, whether the association remains after removing the effects of referral to, or engagement with, psychological care. Methods: We analysed clinical audit data from patients with persistent pain who were quasi-randomly allocated to complete full depression screening using the Patient Health Questionnaire-9 (PHQ-9) or a pain-knowledge questionnaire. The primary outcome was depressive symptoms at 6-month follow-up, using a validated single-item 0 to 10 mood rating scale. Causal mediation analysis estimated the direct effect of depression screening on follow-up mood by blocking effects of referral to, and engagement with, psychological care. Results: A total of 1779 participants (age mean ± SD = 42.7 ± 11.1 years; pain duration mean ± SD = 54.3 ± 29.9 months) were included. At 6-month follow-up, mood numerical rating scale scores improved in both groups (PHQ-9 group n = 886 = -1.3 points SD = 1.3; pain-knowledge questionnaire group n = 893 = -2.0 points SD = 1.8); the PHQ-9 group reported less improvement (mean difference = 0.7/10 points, 95% CI = 0.5-0.8). When referral for (n = 646) and engaging with psychological care (n = 466) were blocked, the direct effect remained (0.5/10 points, 95% CI = 0.3-0.6, 0.4/10 points, 95% CI = 0.2-0.6; respectively). Conclusion: Exposure to screening had smaller reduction in depressive symptoms 6 months later than those who completed a pain-knowledge questionnaire, regardless of referral for, or engagement with, psychological care. Future research should examine how assessment processes influence patient sense-making, clinician responses, and referral pathways in pain care.