We commend and read with interest the difference-in-differences (DiD) study by Lee et al. (1) examining the effect of Medicaid expansion on individuals with diabetes and the management of their disease. Lee et al. reported significant improvements in self-reported access to care, diabetes management frequency, and health status among people with diabetes in states that expanded Medicaid compared with those that did not.
Our first point is about the variables used to define self-reported diabetes management. We recently reported—also using data from the Behavioral Risk Factor Surveillance System—that Medicaid expansion was not associated with a significant increase in dilated eye examinations among patients with diabetes (2). We believe that dilated eye examinations are an important aspect of diabetes care, and survey data demonstrates that people with diabetes report vision loss as a significant, underestimated impact on quality of life (3). Additionally, the lack of a significant increase in eye examinations found in our study highlights an important point: Medicaid expansion may have had a disparate impact on different diabetes care indicators and Medicaid insurance coverage may be insufficient for some measures. Dilated eye examinations, in particular, require patients to see specialists who may be limited in availability or less likely to accept patients with Medicaid insurance. Lee et al. reported an overall increase in an aggregate of factors defined as self-reported diabetes management. Analysis of individual factors within this composite measure may reveal differential effects of Medicaid expansion. For example, insurance coverage may be more efficacious in improving access to doctor visits for consultation or hemoglobin A1c monitoring but less so in increasing the frequency of self-feet checks. Further work analyzing why Medicaid expansion impacts certain diabetes care behaviors more than others will be helpful in identifying areas requiring further intervention.
Our second point is that more granular analysis of temporal trends in DiD studies can reveal additional information about the prolonged impact of a policy change. For example, Sommers et al. (4) found that while Medicaid expansion was associated with a significant increase in reported glucose checks among patients with diabetes in 2015, this increase was not evident in the following year. Similarly, we found that while Medicaid expansion was associated with a significant increase in diabetic eye examinations in the first 2 years after expansion, the increase became nonsignificant when 2016 and 2017 were included in the postexpansion period. In the case of Medicaid expansion, it is plausible that patients with new insurance coverage were referred for screening during intake appointments but were unaware of the necessity of continued interval screening, particularly because the benefits of screening for insidious conditions secondary to chronic diabetes, such as diabetic retinopathy, are not evident. Identification of diminishing impacts of policy effects can be important in prompting new intervention efforts such as patient and provider education, which have been shown to improve diabetes screening adherence (5). We believe that future DiD studies examining the effects of Medicaid expansion should, when possible, examine the effects of a policy change on varying postexpansion periods.
Duality of Interest. No potential conflicts of interest relevant to this article were reported.