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How to Establish Glucose Targets to Achieve A1c Goals

May 29, 2014

The ADAG study was able to determine the average blood glucose for premeal, postmeal and bedtime readings to achieve a variety of A1c targets….

Now you have an answer for your patients who ask, "What do my blood sugars have to be after meals, before meals, and at bedtime to get an A1c of 5.5%?"

The purpose of the study was to determine the average fasting, postprandial, and bedtime self-monitored blood glucose (SMBG) concentrations associated with specified HbA1c levels using data from the hemoglobin A1C-Derived Average Glucose (ADAG) study.

The ADAG study was a multicenter observational study that used continuous glucose monitoring and SMBG testing to determine the relationship between mean average glucose and HbA1c. They used the SMBG data from 470 of the ADAG study participants (237 with type 1 diabetes and 147 with type 2 diabetes) to determine the average fasting, premeal, 90-min postmeal, and bedtime blood glucose (BG) for predefined target HbA1c groups between 5.5 and 8.5% (37–69 mmol/mol). Tests were used to compare mean BG values between type 1 and type 2 diabetes groups.

Recent diabetes management guidelines specify that treatment goals should be individualized based on age, comorbidities, and duration of disease, with an American Diabetes Association (ADA)/European Association for the Study of Diabetes goal of 7% (53 mmol/mol) or American Association of Clinical Endocrinologists (AACE) goal of 6.5% (48 mmol/mol) in otherwise healthy patients. Although HbA1c is the target, it is measured once every 3 months, and day-to-day self-management of diabetes to achieve and maintain the individualized target HbA1c is facilitated by self-monitored blood glucose (SMBG) values, especially in patients treated with insulin.

To achieve the recommended HbA1c goals, the ADA, the European Association for the Study of Diabetes, the AACE, and the International Diabetes Federation (IDF) have recommend SMBG targets, the origins of which are obscure but appear to be based predominantly on expert opinion. As a result, there is wide variation in the recommended SMBG targets to achieve an HbA1c of 7% (53 mmol/mol) and little to guide clinicians and patients on how to achieve other, individualized, targets.

With the publication of the DCCT results in 1993, recommendations for SMBG targets were based largely on the DCCT protocol in which SMBG targets were 70–120 mg/dL preprandial and 180 mg/dL postprandial. Currently recommended SMBG targets appear to be largely based on expert opinion or from extrapolations from regression equations comparing the mean of all the daily capillary-measured plasma glucose levels, independent of the distribution during the day, and HbA1c.

The consequences of using the previously published, nonempirical data may include pushing patients harder to achieve lower fasting levels than are actually required.

The target BG levels necessary to achieve specified HbA1c values were generally similar for type 1 and type 2 diabetes patients, endorsing a similar set of target values regardless of type of diabetes in nonpregnant adults. While there were statistically significant differences between prelunch and postbreakfast BG averages compared with other meals within an HbA1c group, clinically these differences are small (15% difference within an HbA1c group), and it would be reasonable to apply the aggregate premeal and aggregate postmeal BG values for all meals.

A strength of the ADAG study in addressing BG targets is that it included people with a wide range of stable HbA1c values from many different communities. Although the BG measurements over the course of the 12-week study were measured in a structured way (before meals and 2 h after meals), the timing of measurements was dictated by the participants real-life environment and schedule. Both a strength and a limitation of this study is that the BG measurements were obtained with a laboratory-quality point-of-care glucose monitoring device, which may give somewhat more precise and accurate BG measurements than usual consumer SMBG devices, something that will need to be accounted for when extrapolating these results to clinical practice. The relatively small numbers of type 2 diabetes patients, especially at the higher HbA1c ranges, resulted in larger CIs for this subgroup, but with the exception of postprandial mean BG in the highest HbA1c target range of 8.0–8.5%, the mean values between type 1 and type 2 diabetes patients were similar (15% difference within an HbA1c group), and they chose to present the aggregate data.

The choice of glucose monitoring schedule and goals remains complex, predicated on target HbA1c, treatment regimens, risk of hypoglycemia, and cost-effectiveness. For patients and providers, setting appropriate day-to-day BG testing goals to achieve a specific and individualized HbA1c target is important to guide the patient’s self-care and self-management. The current study establishes realistic target BG levels, based on empirical data, to inform our patient-centered care. The researchers hope that these data will be used by professional societies, clinicians, and patients to guide the appropriate choice of glucose targets and treatment to achieve their individualized HbA1c goal. See this week’s Tool for Your Practice to calculate what your patients’ blood sugars need to be to achieve a specific A1c.

Practice Pearls:
  • There is wide variation in the recommended SMBG targets to achieve a specific HbA1c
  • Recent diabetes management guidelines specify that treatment goals should be individualized based on age, comorbidities, and duration of disease
  • The empirical data and the results will help patients achieve individualized HbA1c levels.

Published online before print February 10, 2014, doi: 10.2337/dc13-2173 Diabetes Care February 10, 2014