Self-monitoring of blood glucose (SMBG) is a major advance in diabetes care, but questions remain about its exact role in type 2 diabetes (1). Studies conducted in large clinical practices have shown a positive association between SMBG frequency and good glycemic control in patients with type 2 diabetes. However, few attempts to describe the relationship between monitoring and glycemic control have looked beyond the frequency of testing to determine whether patients clearly understood their target values and how they respond to the information obtained from monitoring (24).

In a collaborative effort, the Great Falls Clinic and the Montana Department of Public Health and Human Services surveyed a random sample of current patients with diabetes (815 of 1,234 patients were selected) by telephone in October 2002, to assess their diabetes care. Respondents were asked if they were currently taking insulin and/or oral antihyperglycemic medications and were classified into three groups: those using insulin with or without oral antihyperglycemic agents, those taking oral therapies only, and those not currently taking any diabetes medications. Respondents were also asked about SMBG, “About how often do you check your blood for glucose or sugar?” (the response categories for this question were the number of times per day, week, month, or year, or don’t know/not sure, never, and refused to answer). Respondents reporting any SMBG were then asked, “What do you do with your blood glucose or sugar readings when they are too high? Do you adjust your medication? Do you eat less food?” Respondents who monitored were also asked, “What do you do with your blood glucose or sugar readings when they are too low? Do you adjust your medication? Do you take more food?” And finally, those who reported any SMBG were asked, “What is your target blood glucose or sugar value?”

The most recent A1c values were matched to the information collected from the telephone survey. A1c testing was performed by a central laboratory using the BioRad Variant II (BioRad, Hercules, CA), a high-pressure liquid chromatography method (normal range 4.0–6.0%). Data analyses were conducted using SPSS v10.0 software. Pearson χ2 tests were used to compare SMBG practices by medication type, and Kruskal-Wallis tests were used to compare the median A1c value among respondents by SMBG target and medication type. Nonparametric statistical tests were used in these analyses because the A1c values were not normally distributed.

Of the 815 patients, 61% completed the survey. There were no statistically significant differences between respondents and nonrespondents by age (mean age 62.3 vs. 61.5 years, P = 0.49), sex (male 55 vs. 48%, P = 0.07), or by the last A1c value (median A1c value 7.2 vs. 7.3%, P = 0.12). Thirty-seven percent of respondents used insulin (27% insulin alone and 10% in combination with oral agents), 49% used oral medications only, and 14% were taking no antihyperglycemic medications. Respondents using insulin were more likely to monitor daily (52%) compared with those taking oral medication only (30%) and those taking no medication (7%, P < 0.001). Those using insulin were also more likely to report an SMBG target (88%) compared with respondents taking oral therapy only (70%) or those taking no medication (42%, P < 0.001).

Among respondents using insulin, a larger proportion of those reporting a blood glucose target took some action (i.e., adjusted medication and/or ate more/less food) when their blood glucose values were low compared with those without a target (90 vs. 71%, P = 0.02). However, there were no differences between the two groups regarding actions taken when the glucose values were high (86 vs. 77%, P = 0.27). Among respondents taking oral medications only, those with a blood glucose target were also more likely than those without a target to take some action when their blood glucose values were low (63 vs. 46%, P = 0.03), but not when they were high (65 vs. 64%, P = 0.82). For respondents taking no medications, those with blood glucose targets were no more likely to take any action (i.e., eat more/less food) when their blood glucose values were high (67 vs. 33%, P = 0.06) or low (50 vs. 40%, P = 0.57) compared with those who did not report a target.

The median target blood glucose value reported was 120 (25th percentile = 105, 75th percentile = 130). Individuals using insulin reporting targets ≤120 had a significantly lower median A1c values (median 7.3%) compared with those with SMBG targets >120 (8.3) and those with no target (8.7, P = 0.02). There was a small but not significant difference in the median A1c values among respondents taking oral medications in those with targets ≤120 (7.1) compared with those reporting targets >120 (7.3) or those with no target (7.0, P = 0.07). But, there were no differences in the median A1c values regardless of a reported target or the level of the target among those taking no diabetes medications (6.1 for each medication group, P = 0.29).

This is one of very few studies to look beyond the frequency of SMBG and ask how patients understood and utilized their values before looking at the relationship of monitoring to glycemic control. Many patients with diabetes who monitored did not know their blood glucose targets. Among those taking insulin, lower targets were clearly associated with better metabolic control. The relationships between targets and metabolic control were not as clear among patients taking only oral medications or those taking no medications. However, our sample was small, and we could not distinguish recently diagnosed individuals from long-term patients. The cross-sectional design of this study precludes determining whether awareness of glycemic targets led to better glycemic control versus achievable targets that were tailored to each patient’s level of glycemic control (e.g., patients in poor control were given high and more achievable glycemic targets by their provider). Longitudinal studies are needed to address this issue.

Thus, the role of SMBG in type 2 diabetes will likely depend on both the therapies used to control hyperglycemia and what both patients and health care providers do with the values. Finally, the SMBG frequency for individuals with type 2 diabetes to maintain optimal A1c levels for a given therapy may be different from the frequency needed to adjust therapy to reach a target. (5) We have previously shown that patients with diabetes did not always know their A1c value or its meaning (6). Similarly, in this study patients with diabetes did not always have a clear understanding of what blood glucose levels they should be trying to achieve.

This project was supported through cooperative agreements (U32/CCU815663-05) with the Centers for Disease Control and Prevention, Division of Diabetes Translation, Atlanta, Georgia. The contents of this report are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.

We thank Linda Priest and the staff members of Northwest Resource Consultants for their expertise and work on the telephone survey. We also thank Susan Day for her assistance throughout this project.

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D.G. has received honoraria or consulting fees from NovoNordisk, Aventis, and GlaxoSmithKline.