Health care costs before and after diagnosis of depression in patients with unexplained pain: a retrospective cohort study using the United Kingdom General Practice Research Database

Purpose: To assess the impact of pain severity and time to diagnosis of depression on health care costs for primary care patients with pre-existing unexplained pain symptoms who subsequently received a diagnosis of depression. Patients and methods: This retrospective cohort study analyzed 4000 adults with unexplained pain (defined as painful physical symptoms [PPS] without any probable organic cause) and a subsequent diagnosis of depression, identified from the UK General Practice Research Database using diagnostic codes. Patients were categorized into four groups based on pain severity (milder or more severe; based on number of pain-relief medications and use of opioids) and time to diagnosis of depression (≤ year or >1 year from PPS index date). Annual health care costs were calculated (2009 values) and included general practitioner (GP) consultations, secondary care referrals, and prescriptions for pain-relief medications for the 12 months before depression diagnosis and in the subsequent 2 years. Multivariate models of cost included time period as a main independent variable, and adjusted for age, gender, and comorbidities. Results: Total annual health care costs before and after depression diagnosis for the four patient groups were higher for the groups with more severe pain (£819-£988 versus £565-£628; P,<0.001 for all pairwise comparisons) and highest for the group with more severe pain and longer time to depression diagnosis in the subsequent 2 years (P,<0.05). Total GP costs were highest in the group with more severe pain and longer time to depression diagnosis both before and after depression diagnosis (P,<0.05). In the second year following depression diagnosis, this group also had the highest secondary care referral costs (P,<0.01). The highest drug costs were in the groups with more severe pain (P,<0.001), although costs within each group were similar before and after depression diagnosis. Conclusion: Among patients with unexplained pain symptoms, significant pain in combination with longer time from pain symptoms to depression diagnosis contribute to higher costs for the UK health care system.