Association of Numeracy and Diabetes Control

To the editor: In reviewing the findings of Cavanaugh and colleagues,(1) we were impressed that the association between low numeracy and poor glycemic control appeared much stronger among insulin users than among those taking oral medications. In addition, their finding that low- numeracy insulin users were less likely than high-numeracy insulin users to self-adjust insulin dosage and count carbohydrates provides a possible mechanism. This would suggest that not only does numeracy affect quality, but may also have important implications for patient safety. Hypoglycemia relating to insulin use is a leading cause of adverse drug events leading to emergency department visits(2), and we have found that diabetes patients who report having problems learning about their health due to reading difficulties have higher incidence of severe hypoglycemia episodes (3). Taken together, this research suggests that system-level interventions to mitigate the effects of limited literacy and low numeracy must involve some combination of (a) providing adequate self-management support regarding insulin, (b) developing individualized glycemic targets; and (c) proactive surveillance(4) for adverse drug events related to insulin.

1. Cavanaugh K, Huizinga MM, Wallston KA, et al. Association of numeracy and diabetes control. Ann Intern Med. 2008;148(10):737-46.

2. Budnitz DS, Shehab N, Kegler SR, Richards CL. Medication use leading to emergency department visits for adverse drug events in older adults. Ann Intern Med. 2007;147(11):755-65.

3. Sarkar U, Karter A, Adler N, Liu J, Moffet H, Schillinger D. Limited health literacy is associated with increased risk of hypoglycemia among insured, type 2 diabetes patients: the Diabetes Study of Northern California (DISTANCE). Society for General Internal Medicine. Pittsburgh, PA: Journal of General Internal Medicine; 2008: 23(s2): 338.

4. Sarkar U, Handley M, Gupta R, et al. Use of an interactive, telephone-based self-management support program to identify adverse events among ambulatory diabetes patients. Journal of General Internal Medicine. 2008;23(4):459-65.

Conflict of Interest:

None declared

We agree that interventions to reduce the frequency and severity of hypoglycemic episodes in patients are an integral component of diabetes care and patient safety. Patient literacy and numeracy may play an important role in adverse events related to blood sugar management. For a subgroup of patients in our study (n=163, 41% of the primary sample), we were able to download their blood glucose meters and obtain information about the frequency of hypoglycemic events (defined as blood glucose<60 mg/dL) and the proportion of blood glucose measures less than 70 mg/dL. The majority of these patients (58%) did not have a measured hypoglycemia event, however 42% recorded at least one event and 10% of these patients had more than 5 events recorded. While patients with Type 1 diabetes (n=42) were more likely to have hypoglycemia events than patients with Type 2 diabetes (n=121) (86% vs. 27%; p<0.0001), neither health literacy or diabetes-related numeracy was associated with the number of hypoglycemia events as measured by self-blood glucose monitoring in either type of diabetes. Health literacy or diabetes-related numeracy were also not found to be significantly associated with proportion of blood glucose meter readings that were low (<70 mg/dL). Results were also similar if patients only using insulin (n=121) were included in the analysis. This subgroup evaluation was significantly limited by its small, selected sample of patients, and was not adequately powered to evaluate this important question. It is possible that patients with lower numeracy may have had higher rates of hypoglycemic episodes, but did not record these episodes with their glucose meter, or did not bring their meter to clinic for download. Additional, larger studies are needed to define the role of literacy and numeracy in the prevention of serious adverse events and overall safety of patients with diabetes and other chronic diseases.

Conflict of Interest:

None declared