The use of insulin declines as patients live farther from their source of care: results of a survey of adults with type 2 diabetes

Abstract

Background: Although most diabetic patients do not achieve good physiologic control, patients who live closer to their source of primary care tend to have better glycemic control than those who live farther away. We sought to assess the role of travel burden as a barrier to the use of insulin in adults with diabetes.

Methods: 781 adults receiving primary care for type 2 diabetes were recruited from the Vermont Diabetes Information System. They completed postal surveys and were interviewed at home. Travel burden was estimated as the shortest possible driving distance from the patient's home to the site of primary care. Medication use, age, sex, race, marital status, education, health insurance, duration of diabetes, and frequency of care were self-reported. Body mass index was measured by a trained field interviewer. Glycemic control was measured by the glycosolated hemoglobin A1C assay.

Results: Driving distance was significantly associated with insulin use, controlling for the covariates and potential confounders. The odds ratio for using insulin associated with each kilometer of driving distance was 0.97 (95% confidence interval 0.95, 0.99; P = 0.01). The odds ratio for using insulin for those living within 10 km (compared to those with greater driving distances) was 2.29 (1.35, 3.88; P = 0.02).

Discussion: Adults with type 2 diabetes who live farther from their source of primary care are significantly less likely to use insulin. This association is not due to confounding by age, sex, race, education, income, health insurance, body mass index, duration of diabetes, use of oral agents, glycemic control, or frequency of care, and may be responsible for the poorer physiologic control noted among patients with greater travel burdens.

Figure 1

Distribution of driving distances for insulin users and non-users. The middle line of each box represents the median driving distance. The boxes span the inter-quartile range of driving distances from the 25^th to the 75^th percentiles. The whiskers span the outer quartiles. Outlier or outside values are excluded so that the medians and quartiles can better be compared.

Figure 2

Insulin use over the range of driving distances. Driving distances were divided into quartiles of 195 or 196 subjects each. The heights of the bars represent the proportion of subjects in each quartile who use insulin.