Racial and Regional Disparities in Outcomes Among Veterans Initially Adherent to Oral Antidiabetic Therapies: an Observational Cohort Study

Abstract

Background: Adherence to prescribed medications is connected with, but is not a guarantee of, improved disease management and health outcomes. It remains unclear whether underlying health disparities exist among patients adherent to therapy and whether differences in outcomes vary by race and residential areas of the country.

Objective: To determine the extent of racial and regional variation in outcomes within 5 years of oral antidiabetic drug initiation among veterans adherent to therapy.

Design: Retrospective cohort study of 83,265 US Veterans Health Administration data, 2002-2014 PATIENTS: US veterans with uncomplicated diabetes and taking oral antidiabetic agents MAIN MEASURES: Veterans initially adherent to oral antidiabetic therapy were followed for up to 5 years, and comparisons focused on differences between non-Hispanic White and non-Hispanic Black veterans across geographic region and residential type (urban or rural). Outcomes included composite cardiovascular events, composite cerebrovascular events, or all-cause mortality using Poisson and adjusted Cox proportional hazards models.

Key results: Cardiovascular event and all-cause mortality rates differed by race and region, while urban/rural differences were evident for cerebrovascular events and all-cause mortality. For non-Hispanic Blacks, the mortality rate was half that compared to non-Hispanic Whites (6.5 [95% CI 5.8-7.2] versus 13.3 [95% CI 12.9-13.8], p < 0.0001). Compared to the Northeast, all other regions had higher adjusted hazards for cardiovascular or cerebrovascular events (with a single exception), but no regional differences in all-cause mortality were observed. Models with interactions demonstrated that racial differences in cardiovascular events and all-cause mortality were isolated to the Midwest (HR 1.99 [95% CI 1.301-3.06; HR 1.64 [95% CI 1.210-2.215]) and South (HR 1.69 [85% CI 1.347-2.131]; HR 1.27 [95% CI 1.095-1.470]).

Conclusions: Despite adherence to therapy, differences in outcomes are likely among veterans with diabetes based on race and geography. Localized analyses may uncover specific social determinants contributing to differences in outcomes.

Keywords: adherence; diabetes; racial disparities; regional variation.

Figure 1

Adjusted hazard ratios for health outcomes within the first 5 years of oral antidiabetic medication use footnote: All models controlled for sex, marital status, age, CCI, median zip code income, baseline hemoglobin A1C, BMI, initial OAD, baseline systolic blood pressure, baseline LDL levels, whether the patient filled a lipid-lowering drug as of the first year of OAD use, and whether the patient filled an antihypertensive medication as of the first year of OAD use. Additionally, models controlled for record of a prior CAD or CVD event prior to initiating OAD treatment.

Figure 2

Within-region racial and residential differences in adjusted hazards for health outcomes within the first 5 years of oral antidiabetic medication use footnote: All models controlled for sex, marital status, age, CCI, baseline hemoglobin A1c, BMI, initial OAD, baseline systolic blood pressure, baseline LDL, and whether the patient filled an antihypertensive medication and/or a lipid-lowering drug as of the first year of OAD use. Additionally, models controlled for record of a prior CAD or CVD event prior to initiating OAD treatment. Interactions between region and race and urban/rural were included to determine within-region differences variation by race and residential type. Bolded values indicate statistical significance at p < 0.05. *Compared to urban residents. **Compared to non-Hispanic Black veterans with diabetes. NHW: non-Hispanic White.