Unique characteristics of high-cost users of medical care with comorbid mental illness or addiction in a population-based cohort

Objective — To understand if high-cost users of medical care with and without comorbid mental illness or addiction differ in terms of their sociodemographic and health characteristics. Unique characteristics would warrant different considerations for interventions and service design aimed at reducing unnecessary healthcare utilization and associated costs.

Methods — From the top 10% of Ontarians ranked by total medical care costs during fiscal year 2011/12 (N=314,936), prior 2-year mental illness or addiction diagnoses were determined from administrative data. Sociodemographics, medical illness characteristics, medical costs and utilization were compared between those high-cost users of medical care with and without comorbid mental illness or addiction. Odds of being a frequent user of inpatient (≥3 admissions) and emergency (≥5 visits) services were compared between groups, adjusting for age, sex, socioeconomic status and medical illness characteristics.

Results — High-cost users of medical care with comorbid mental illness or addiction were younger, lower socioeconomic status, had greater historical medical morbidity, and had higher total medical care costs (mean excess of $2,031/user) than those without. They were more likely to be frequent users of inpatient (12.8% vs. 10.2%; adjusted OR 1.14, 95% CI 1.12–1.17) and emergency (8.4% vs. 4.8%; adjusted OR 1.55, 95%, 95% CI 1.50–1.59) services. Effect sizes were larger in major mood, psychotic and substance use disorder subgroups.

Conclusions — High-cost medical care users with mental illness or addiction have unique characteristics with respect to sociodemographics and service utilization patterns to consider in interventions and policies for this patient group.