Objective: The study examined whether comorbid low mental health functioning inflates the cost of treating a chronic disease.
Methods: Data were from the 2015 Medical Expenditure Panel Survey (N=33,893). Costs were estimated from medical records and self-reported health care use. The mental component summary (MCS) score of the 12-item Short Form (SF-12) was used as a measure of mental health status. A general linear model estimated costs with fixed effects for chronic disease (present or absent) and mental health functioning (lowest, middle, and highest MCS score tertiles indicating low, middle, and high levels of mental health functioning, respectively). The SF-12 physical component summary score was a covariate. Eight conditions (arthritis, chronic obstructive pulmonary disease [COPD], high cholesterol, cancer, diabetes, stroke, coronary heart disease, and asthma) were analyzed separately.
Results: For each analysis, presence or absence of the chronic condition had a strong impact on cost. Lower mental health functioning also had a significant impact on cost. However, the interaction between mental health functioning and chronic disease diagnoses was statistically significant for only three conditions and accounted for only a small variation in cost. Sensitivity analyses using MCS score as a continuous variable, using a log10 transformation of the cost variable, and focusing only on persons with scores on the extreme low end did not significantly alter the conclusions.
Conclusions: Contrary to expectation, the combination of poor mental functioning and chronic disease diagnosis did not have a strong synergistic effect on cost. Mental and general medical conditions appear to have independent effects on health care costs.
Keywords: Collaborative care; Cost; Depression; Mental health.