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Original Research |

Association of Numeracy and Diabetes Control

Kerri Cavanaugh, MD, MHS; Mary Margaret Huizinga, MD, MPH; Kenneth A. Wallston, PhD; Tebeb Gebretsadik, MPH; Ayumi Shintani, PhD, MPH; Dianne Davis, RD, CDE; Rebecca Pratt Gregory, RD, CDE; Lynn Fuchs, PhD; Robb Malone, PharmD, CDE; Andrea Cherrington, MD, MPH; Michael Pignone, MD, MPH; Darren A. DeWalt, MD, MPH; Tom A. Elasy, MD, MPH; and Russell L. Rothman, MD, MPP
[+] Article, Author, and Disclosure Information

From Vanderbilt University School of Medicine and Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee; University of North Carolina, Chapel Hill, North Carolina; and University of Alabama, Birmingham, Alabama.

Grant Support: From the American Diabetes Association (Novo Nordisk Clinical Research Award), the Pfizer Clear Health Communication Initiative, and the Vanderbilt Diabetes Research and Training Center (National Institute of Diabetes and Digestive and Kidney Diseases [NIDDK] 5P60DK020593). Dr. Rothman is also currently supported by an NIDDK Career Development Award (NIDDK 5K23DK065294).

Potential Financial Conflicts of Interest:Honoraria: D.A. DeWalt (Pfizer), R.L. Rothman (Pfizer). Grants received: D.A. DeWalt (Pfizer), R.L. Rothman (Pfizer).

Reproducible Research Statement:Study protocol, statistical code, and data set: Available, with institutional approval, from Dr. Rothman (e-mail, russell.rothman@vanderbilt.edu).

Requests for Single Reprints: Russell L. Rothman, MD, MPP, Vanderbilt University Medical Center, 6100 Medical Center East, North Tower, Vanderbilt Center for Health Services Research, Nashville, TN 37232-8300; e-mail, russell.rothman@vanderbilt.edu.

Current Author Addresses: Dr. Cavanaugh: Vanderbilt University, 1161 21st Avenue South, 5-3223 Medical Center North, Nashville, TN 37232.

Drs. Huizinga and Rothman: Vanderbilt University, 1215 21st Avenue South, 6100 Medical Center East, North Tower, Nashville, TN 37232.

Dr. Wallston: Vanderbilt University, 421 Godchaux Hall, 461 21st Avenue South, Nashville, TN 37240.

Drs. Gebretsadik and Shintani: Vanderbilt University, 1211 21st Avenue South, S-2323 Medical Center North, Nashville, TN 37232.

Dr. Davis: Vanderbilt University, 1211 21st Avenue South, 3061 Medical Arts Building, Nashville, TN 37212.

Dr. Pratt Gregory: Vanderbilt University Diabetes Center, 315 Med Arts, 1211 21st Avenue South, Nashville, TN 37212.

Dr. Fuchs: Vanderbilt University, 228 Peabody, 230 Appleton Place, Nashville, TN 37220.

Drs. Malone, Pignone, and DeWalt: University of North Carolina Chapel Hill, 5039 Old Clinic Building CB #7110, Chapel Hill, NC 27599.

Dr. Cherrington: University of Alabama, 1530 3rd Avenue South, Birmingham, AL 35294.

Dr. Elasy: Vanderbilt University, 1215 21st Avenue South, 8210 Medical Center East, South Tower, Nashville, TN 37232.

Author Contributions: Conception and design: R.L. Rothman, K.A. Wallston, R. Pratt Gregory, L. Fuchs, D.A. DeWalt, T.A. Elasy.

Analysis and interpretation of the data: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, T. Gebretsadik, A. Shintani, M. Pignone, D.A. DeWalt.

Drafting of the article: R.L. Rothman, K. Cavanaugh, A. Cherrington.

Critical revision of the article for important intellectual content: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, K.A. Wallston, T. Gebretsadik, R. Malone, A. Cherrington, M. Pignone, D.A. DeWalt, T.A. Elasy.

Final approval of the article: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, K.A. Wallston, L. Fuchs, R. Malone, A. Cherrington, M. Pignone, D.A. DeWalt, T.A. Elasy.

Provision of study materials or patients: R.L. Rothman, K.A. Wallston, D. Davis, R. Malone, M. Pignone.

Statistical expertise: T. Gebretsadik, A. Shintani.

Obtaining of funding: R.L. Rothman.

Administrative, technical, or logistic support: R.L. Rothman, R. Malone, T.A. Elasy.

Collection and assembly of data: R.L. Rothman.

Ann Intern Med. 2008;148(10):737-746. doi:10.7326/0003-4819-148-10-200805200-00006
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This study demonstrates that low diabetes-related numeracy skills are common in patients with diabetes and are associated with lower diabetes knowledge and perceived self-efficacy. In patients who use insulin, low diabetes-related numeracy was also associated with less participation in self-management behaviors. Finally, low diabetes-related numeracy was modestly associated with worse glycemic control.

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Grahic Jump Location
Figure 1.
Examples of Diabetes Numeracy Test items and proportion of correct responses.
Grahic Jump Location
Grahic Jump Location
Figure 2.
Scatterplot of Diabetes Numeracy Test score and hemoglobin A1c level.

The solid line is the best fitted line associating Diabetes Numeracy Test score and hemoglobin A1c. The dotted lines represent the 95% CI.

Grahic Jump Location




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Submit a Comment/Letter
Safety Implications of Low Numeracy
Posted on June 10, 2008
Urmimala Sarkar
University of California, San Francisco
Conflict of Interest: None Declared

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

Numeracy and hypoglycemia events
Posted on July 17, 2008
Kerri Cavanaugh
Vanderbilt University Medical Center
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

Submit a Comment/Letter

Summary for Patients

Association of Numeracy and Diabetes Control

The summary below is from the full report titled “Association of Numeracy and Diabetes Control.” It is in the 20 May issue of Annals of Internal Medicine (volume 148, pages 737-746). The authors are K. Cavanaugh, M.M. Huizinga, K.A. Wallston, T. Gebretsadik, A. Shintani, D. Davis, R. Pratt Gregory, L. Fuchs, R. Malone, A. Cherrington, M. Pignone, D.A. DeWalt, T.A. Elasy, and R.L. Rothman.


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