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To the Editor: Glycated or glycosylated hemoglobin (HbA1c) levels have been used in planning and assessing the management of diabetic patients for the past couple of decades. Clinical trials have established the correlation between HbA1c and the development of diabetes complications and patient outcomes.1,2 HbA1c results are expressed as the percentage of hemoglobin that is glycated and reflects the average blood glucose control over a period of approximately three months. In contrast, blood glucose levels are expressed in milligrams per deciliter and are used for daily monitoring by the patient and healthcare professionals. The discrepancy between HbA1c and blood glucose level units has been problematic and has created some confusion among patients. To reduce this confusion, researchers have determined and reported a linear correlation between HbA1c and self-monitored glucose levels obtained by frequent fingerstick capillary glucose testing and continuous glucose monitoring. A mathematical relationship between the average glucose level over the preceding three months and levels of HbA1c has been established,3 resulting in the translation of HbA1c results into estimated average glucose (eAG). This approach was adopted by the American Diabetes Association (ADA).4,5
The estimated average glucose (eAG) converts the diabetic patient's HbA1c percentage point into an average blood glucose level in the units of measure seen by the patient on glucose meters for daily self-monitoring (mg/dL). Similar to HbA1c, eAG evaluates a patient's overall success at controlling glucose levels and helps patients understand the monitoring of their long-term treatment. The relationship and association between HbA1c and eAG has been supported by several studies with the largest being published by the HbA1c-Derived Average Glucose (ADBG) Study Group.3 The ADAG linear regression formula that is used to calculate the eAG from A1c results is: “28.7×A1c-46.7”, and therefore, every one percent increase in HbA1c is approximately equivalent to an increase of 29 mg/dL in eAG (Table 1).4,6
As a clinical pharmacist practising in an ambulatory care setting, I have noted that patients find it difficult to explain and relate the HbA1c percentage of hemoglobin that is glycated to glucose measurements that they encounter through home or lab glucose monitoring (“numbers are not matching”). Since the introduction of eAG, I have used it to describe three-month blood glucose control in an easily comprehensible way that can be correlated to their home glucose testing. As a first impression, patients appear to quickly accept and welcome eAG. With eAG, patients will have a better understanding of glucose monitoring and can now correlate the results of HbA1c to eAG. Due to the added advantage that eAG brings to patient care, we expect that future consensus guidelines will recommend that laboratories report calculated eAG levels along with A1c values.
The authors acknowledge the use of Saudi Aramco Medical Services Organization (SAMSO) facilities for research data utilized in this manuscript. Opinions expressed in this article are those of the authors and not necessarily of SAMSO.