Burden of health comorbidities and associated health care costs in the Australian genetics of depression study using the medication-based Rx-risk comorbidity index.

Depression is associated with substantial multimorbidity and elevated healthcare utilization. This study characterised treated comorbidities and healthcare costs in participants of the Australian Genetics of Depression Study (AGDS) using pharmaceutical claims data. Linked Pharmaceutical Benefits Scheme (PBS) records from 01/07/2013-31/12/2017 were available for 15,890 AGDS participants. Forty-six chronic conditions were inferred using the validated pharmacy-based Rx-Risk Comorbidity Index based on Anatomical Therapeutic Chemical Classification System codes and PBS item codes. Prevalence estimates were compared with a 4:1 matched non-depressed Australian representative population sample (10PCT) with PBS claims data available from 01/07/2010-31/12/2014. AGDS participants had a higher mean number of inferred comorbidities (4.6 ± 2.9) than individuals in the 10PCT sample (2.0 ± 2.1). Excluding depression, 89.1% of AGDS participants had at least one inferred comorbidity, most commonly pain (51.0%), inflammation/pain (40.3%), and anxiety (32.3%). Metabolic and cardiovascular conditions frequently co-occurred (13.2%). Within AGDS, comorbidity burden was higher among women and increased with age, body mass index, number of depressive episodes and symptoms, and annual healthcare costs. Median annual healthcare costs were approximately 65% higher among AGDS participants with 2-3 inferred comorbidities compared with those with none. This study provides a detailed description of treated comorbidities and associated healthcare costs among Australians living with depression. The findings highlight the substantial multimorbidity burden in this cohort and its association with increased healthcare costs to both the individual and health system.