Comparative Study of Estimated Average Plasma Glucose (eFPG) from HbA1c Level and Fasting Plasma Glucose Level (FPG) in Diabetic Patients at Sakon Nakhon Hospital

Abstract

             This retrospective descriptive study aimed to compare the estimated fasting plasma glucose (eFPG) derived from HbA1c levels with the actual fasting plasma glucose (FPG) in diabetic patients at Sakon Nakhon Hospital. The study included 310 diabetic patients who had same-day test results for HbA1c and FPG. eFPG was calculated using the formula eFPG (mg/dL) = (28.7 × HbA1c) - 46.7, The correlation between eFPG and FPG was analyzed using the correlation coefficient, and differences between the two values were tested using the paired t-test.

             The results showed that the mean ± S.D. of eFPG was 185 ± 62 mg/dL, which was higher than the mean FPG of 143 ± 64 mg/dL. A moderate correlation was found between the two values (r = 0.538, P < 0.001). The paired t-test indicated a statistically significant difference between eFPG and FPG (P < 0.001). When analyzing subgroups based on HbA1c levels, the correlation coefficients between eFPG and FPG were r = 0.355 for patients with HbA1c levels between 5.6-6.4% and r = 0.496 for those with HbA1c ≥ 6.5%. Both subgroups exhibited statistically significant differences between eFPG and FPG (P < 0.001).

                These findings suggest that eFPG levels are consistently higher than FPG levels in all study groups. This discrepancy may be due to patients experiencing falsely low fasting glucose levels as a result of dietary control before testing, leading to lower FPG values compared to eFPG. Therefore, incorporating eFPG alongside HbA1c in diabetes assessment may enhance the accuracy of glycemic monitoring and blood sugar control, ultimately reducing the risk of long-term complications.