ESTIMATED AVERAGE GLUCOSE , EAG – A MORE INTUITIVE UNDERSTANDING OF GLYCEMIC CONTROL

Harpreet Kaur Walia 1 and Kamaljeet Kaur 2 . 1. Department of Biochemistry, Maharishi Markandeshwar Medical College & Hospital, Solan. 2. Department of Biochemistry, Government Medical College & Hospital, Chandigarh. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

109 reference method. 4 However, the new method results in lower values expressed in different units (millimoles per mole of unglycated hemoglobin), which may cause confusion for patients and health care providers. 5 The relationship between the mean blood glucose level and the level of HbA1c has been investigated in different studies, and various equations have been obtained. 6,7,8 Using Nathan's regression equation, which has been recommended by the American Diabetes Association (ADA) , the estimated average glucose (eAG) level calculation and its relationship to the fasting plasma glucose (FPG) level were investigated in the present study.

Materials and Methods:-
Retrospective analysis of 1000 patients in the Department of Biochemistry for FPG and HbA1c was done. FPG and HbA1c levels were determined on fully automated analyzer ROCHE MODULAR P 800 using glucose oxidaseperoxidase method and turbidimetric inhibition immunoassay (TINIA), respectively. The eAG levels were calculated using Nathan's regression equation, (28.7 x HbA1c) -46.7 recommended by American Diabetes Association. According to FPG levels, the patients were divided into Group A (FPG<126mg/dl), Group B (FPG 126-200 mg/dl) and Group C (FPG>200 mg/dl).
All statistical analyses were performed using the Statistical Package for Social Sciences (SPSS, version 11.0 for Windows). Data were expressed as the means ± standard deviation of the mean (SD). A p-value <0.05 was accepted as significant. The Pearson correlation coefficient was used to test the correlation between FPG, eAG and HbA1c levels, and independent t-test was used to find the difference between male and female.

Results:-
The mean FPG, eAG, and HbA1c levels in the whole group are presented in Table1. A positive significant correlation was found between FPG and eAG levels for the entire study group (r = 0.8364 , p< 0.0001).
The mean FPG, eAG and HbA1c levels in groups A, B and C are shown in Table1. When the data was split based on FPG it was observed that the three groups showed significant positive correlation with eAG. The eAG levels were higher compared to FPG levels in the three groups.
The mean levels of FPG, eAG and HbA1c were higher in males than in females .However, there was no significant gender difference for the following variables (Table2).

Discussion:-
Monitoring of glycemic status has been considered the cornerstone of diabetes care. The results of monitoring are used to assess efficacy of therapy and to guide adjustments in lifestyle to achieve best possible glucose control. The most common tests used today for this purpose are blood glucose and glycated hemoglobin (HbA1c). 9 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 mg/dl and are used for daily monitoring by the patient and healthcare professionals. The discrepancy between HbA1c and blood glucose level units has always been problematic and has created confusion among patients. To eliminate this confusion , a mathematical relationship has been established translating HbA1c results into estimated average glucose (eAG). In using eAG, HbA1c results can be reported to patients in units they are already familiar with from their experience in self-monitoring. 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. 5 Using the Nathan's regression equation, we calculated the eAG levels of our study group and investigated their relationship with the FPG levels. The eAG levels were positively correlated with the FPG levels. In addition, the decrease in the significant strong correlation coefficient showed that the association depended on the patients' levels of glucose control. As glucose control worsened, the association became stronger. Similar findings were reported by Bozkaya et al. 2 Most patients who come to the clinic for plasma glucose determination pay more attention to fasting and diet rules. The eAG levels in the study group were higher than the FPG levels (93.3%) not only because patients come to the lab in a fasting state but also because the eAG level is reflective of all plasma glucose levels over the previous three months, including the postprandial glucose levels. Our results were in harmony with the previous studies that showed eAG levels being higher than FPG levels, concluding that the eAG and FPG values cannot be used interchangeably. 2,10 The effect of gender on eAG, FPG and HbA1c levels was also studied. Our results revealed lower eAG, FPG and HbA1c levels in females than those of males (Table 2), otherwise this decrease was non-significant. In concordance to our results, a previous study has observed that these variables did not differ significantly between males & females. 10 However, a study reported a significant gender difference with respect to eAG and HbA1c levels. 2 The

Correlation of FPG and eAG in all groups
111 above reported variation can be explained by the difference in the population studies and possibly, the different laboratory methodologies used.
In concordance to the results reported by other studies 2 , the eAG levels of males and females were found to be higher than the FPG levels in most cases ( 92.6% and 94.2% , respectively), similar to the results found for the group as a whole ( 93.3%).
It is thought that diabetic patients require better strategies to improve self-management. 11 One of these strategies is the use of eAG levels together with HbA1c values. 12,13 Although the clinical usefulness of eAG is not clear, it is believed that every patient's eAG level should be calculated and provided in addition to the HbA1c level. This will help patients better understand the importance of keeping their blood glucose levels within acceptable limits and may rescue them from invasive approaches for glucose homeostasis. 14

Conclusion:-
According to our data, patients with good to moderate blood glucose control are not entirely successful at managing their blood glucose, as reflected by their eAG levels, and the association between FPG and eAG levels depends on the extent of glycemic control. The study concludes that there is a positive correlation between eAG and FPG, hence it seems intuitive that the reporting of eAG together with the HbA1c level will assist patients and doctors determine the effectiveness of blood glucose control measures.