Author: Thomas L. Lenz, PharmD, MA, PAPHS; Michael S. Monaghan, PharmD, BCPS; Alan W.Y. Chock, PharmD; and Julie A. Stading, PharmD, CDE
The American Diabetes Association recommends that health care providers incorporate an estimated average glucose measurement when counseling patients with diabetes.
The prevalence of diabetes mellitus is rising to epidemic proportions worldwide. Diabetes is now one of the top 5 causes of death in developed countries and the seventh leading cause of death in the United States.1,2
The risk of mortality in patients with diabetes is twice as high as in those without diabetes. Recent data indicate that the United States falls short of the desired goals for disease control.3
Pharmacists are well positioned within the community to educate patients with diabetes—and to help them reach their treatment goals to reduce diabetes morbidity and mortality.
Recently, the American Diabetes Association (ADA) published a new recommendation for health care providers that will assist them in educating and reeducating patients on the importance of glycemic control and the seriousness of diabetes.4
The ADA now suggests that health care providers incorporate an estimated average glucose (eAG) measurement as a new term when educating patients with diabetes.4
Pharmacists should understand and delineate how this measurement may be used to educate patients with diabetes to help them achieve treatment goals.
Current Methods of Monitoring Diabetes
The ADA recommends self-monitoring of blood glucose (SMBG) and hemoglobin A1C (A1C) measurements as the 2 main strategies for monitoring glycemic control.5
SMBG is performed by patients themselves via a glucometer for the day-to-day management of blood glucose levels. The results of SMBG are presented in unit measurements as either mg/dL or mmol/L. Patients with diabetes are encouraged to record their blood glucose readings in a diary to more closely monitor levels throughout the day. The ADA currently recommends that patients with diabetes aim for a fasting blood glucose level of <130 mg/dL.5
An A1C assay is considered the gold standard for judging the adequacy of diabetes treatment and adjusting therapy based on results. Hemoglobin A (HbA) is the major constituent of total hemoglobin and the A1C reflects the percent of glycated hemoglobin. Hemoglobin A1C subcategory is the predominant form of the Hemoglobin A subtypes. It is irreversibly modified through glycation when hemoglobin is exposed to high levels of glucose in blood.6 Therefore, the A1C is found to be significantly higher in those with uncontrolled diabetes mellitus.7,8
The A1C assay is the gold standard measurement for evaluating glycemic control in diabetes for 2 main reasons. First, unlike SMBG, which only reflects current glucose levels, the A1C reflects glucose control over the previous 6 to 12 weeks based on the approximate 120-day life span of erythrocytes. Second, A1C is predictive of microvascular complications that develop with diabetes, and epidemiologic evidence suggests that it also predicts macrovascular complications. Therefore, the ADA recommends A1C monitoring for long-term glycemic control and estimating the risk of developing complications in both type 1 and type 2 diabetes.9
The A1C assay is recorded as a percentage rather than mg/dL or mmol/L as with blood glucose, and the ADA currently recommends an A1C <7.0% as the goal for most patients with diabetes.10
Estimated Average Glucose
For the past several years, A1C measurements have provided patients and caregivers with a valuable tool for assessing diabetes control. The A1C results, however, are not always easy to explain to patients and can often be confusing in regard to the relationship between A1C and blood glucose measurements obtained from a glucometer. As a result, patients may have difficulty translating A1C goals into actions. Estimated average glucose was developed as a way to express and report A1C values in the same units as used with self-monitoring to enhance patient understanding of diabetes control.11
A recent international multicenter trial called the A1C-Derived Average Glucose (ADAG) study was designed to define a mathematical relationship between A1C and average glucose levels to determine if A1C could be expressed and reported as average glucose in the same units as used in selfmonitoring.12
A total of 507 individuals participated in the study; 268 had type 1 diabetes, 159 had type 2 diabetes, and 80 were nondiabetic. At the end of the 3-month study period, A1C levels were obtained and compared with average glucose readings obtained over the same time. Average glucose measurements were obtained and calculated by combining weighted results from at least 2 days of continuous glucose monitoring performed 4 times throughout the study period. In addition, the participants obtained daily blood glucose measurements via a glucometer 7 times per day on at least 3 days per week during the 3-month study period.12
Approximately 2700 glucose values were obtained from each of the participants.
The results demonstrated a significant relationship between the average glucose and the A1C at the end of the 3-month study period—R2
= .84, P <.0001.12 These results allowed the investigators to develop a mathematical equation to convert A1C values to eAG values expressed as mg/ dL. This conversion equation is as follows: eAG (mg/dL) = 28.7 X A1C – 46.7.
More specifically, the study results demonstrated a significant relationship when forming a linear regression between A1C and the eAG from continuous glucose monitoring (R2
= .82, P <.0001).12
In addition, the A1C and the self-glucose monitoring via a glucometer also demonstrated a significant relationship (R2
= .82, P <.0001). When looking at the participants who only had diabetes, the relationship between A1C and eAG was also shown to be significant (R2
= .79, P <.0001).12
It should be noted, however, that differences may exist within ethnicities, as average calculated glucose levels were lower in African Americans compared with others. The study was not properly powered to evaluate statistical differences between ethnicities.12
No children were involved in the ADAG study, so the use of this equation in children is not supported.
As a result of the ADAG study, the ADA, along with the European Association for the Study of Diabetes and the International Diabetes Federation, support and promote eAG as a tool to educate patients about diabetes control.4
The eAG allows health care providers the ability to report A1C results to patients using the same units (mg/dL or mmol/L) that patients see routinely in self–blood glucose measurements. The ADA also offers an application for public use to convert A1C to eAG and vice versa,4
which can be found on the ADA Web site at http://professional.diabetes.org/glucose calculator.aspx
Implementing eAG in Pharmacy Practice
In clinical practice, an A1C value is helpful in determining if the current therapeutic regimen is working and if changes are needed. However, patients may not understand the significance of the A1C value. Showing patients how the A1C relates to their home glucose monitor readings may help them understand what they need to achieve.
For example, if a patient’s A1C is 8%, this roughly correlates to an eAG of 180 mg/ dL. If the patient were then told that their target A1C is 7% or less, they could relate this value to an eAG of around 155 mg/dL. It could be explained to the patient that he or she would need to reduce the blood glucose readings by an average of roughly 25 mg/ dL. Explaining this information to the patient in this manner provides a target goal that is both understandable and familiar.
Having the research to show a significant correlation between A1C and average glucose, as well as the support of the major diabetes organizations, should lead health care providers, including pharmacists, to implement this new language in practice. Specifically in regard to pharmacy practice, pharmacists can use eAG data with confidence to describe A1C to patients as “an average blood glucose over the last few months.”11
Pharmacists and others have been essentially using this explanation for decades, but it can now be used with confidence. In addition, knowing a patient’s eAG can be beneficial to both the pharmacist and the patient in that the measure of longterm blood glucose control (A1C) can be explained to patients more easily by using the same units as those patients are familiar with from self-monitoring.11
Lastly, pharmacists can use this new information as an opportunity to educate patients and re-address the importance of blood glucose control as well as the seriousness of diabetes.11
Ultimately, the incorporation of eAG as a means of patient education should facilitate the achievement of target A1Cs, and therefore reduce the relative risks of diabetes complications.
Diabetes is a significant health concern and one on which pharmacists can have a positive impact at the patient level. The A1C assay is considered the primary laboratory measurement to assess the effectiveness of a patient’s therapy and to adjust therapy when needed. SMBG levels at home are also an important strategy for patients to use to more adequately control diabetes. Patients may get confused about the relationship between A1C and their self-monitoring values, because these tools do not use the same units of measure. New research now demonstrates a correlation between an eAG value and A1C, which allows patients and health care providers to convert A1C values into the same unit of measure (mg/dL) patients are familiar with from self-monitoring their blood glucose. This new term in diabetes management may help improve patients’ understanding of their diabetes and lead to better health outcomes.
Dr. Lenz is an associate professor in the department of pharmacy practice and director of the Pharmacy Distance Pathway at Creighton University in Omaha, Nebraska. Dr. Monaghan is a professor in and chair of the department of pharmacy practice, Dr. Chock is an assistant professor in the department of pharmacy practice, and Dr. Stading is an associate professor in the department of pharmacy practice at Creighton University in Omaha, Nebraska.
1. Disdier-Flores OM, Rodriguez-Lugo LA, Perez-Perdomo R, Perez-Cardona DM. The public health burden of diabetes: a comprehensive review. PR Health Sci J.
2. National Institute of Diabetes and Digestive and Kidney Diseases. National diabetes statistics, 2007.
Bethesda, MD: National Institute of Health, 2007.
3. Saaddine JB, Engelgau MM, Beckles GL, Gregg EW, Thompson TJ, Narayan KMV. A diabetes report card for the United States: quality of care in the 1990s. Ann Int Med.
4. American Diabetes Association. Estimated average glucose, eAG. 2008. Available at: http://professional.diabetes.org/glucosecalculator.aspx. Accessed on September 27, 2010.
5. American Diabetes Association: Standards of medical care in diabetes—2009. Diabetes Care.
6. Umesh M: Diabetes Mellitus and Hypoglycemia. In CURRENT Medical Diagnosis and Treatment.
McPhee SJ, Papadakis, M.A., Tierney, L.M., Ed., 2009. Available at: www.accessmedicine.com.cuhsl.creighton.edu/content.aspx?aID=15524. Accessed on September 27, 2010.
7. Sacks DB, Bruns DE, Goldstein DE, Maclaren NK, McDonald, JM, Parrott M. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem.
8. Berg AH, Sacks DB. Haemoglobin A1c analysis in the management of patients with diabetes: from chaos to harmony. J Clin Pathol.
9. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care.
10. American Diabetes Association. International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care.
11. Kahn R, Fonseca V. Translating the A1C assay [editorial]. Diabetes Care
12. Nathan D, Kuenen J, Borg R, et al. Translating the A1c assay into estimated average glucose values. Diabetes Care.