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Can Fasting Blood Sugar be Used as an Indicator of Long-Term Diabetic Control Instead of Estimated Average Glucose? by Nabeel Alzahrani, Sultan Alouffi, Khaled Almutairi, Mansour Almutairi, Turki Almutairi, Ibrahim Al Alwan, Nawaf Otaibi, Waleed Tamimi

Background: Diabetes mellitus is a chronic illness that is a worldwide issue. HbA1c has been used to monitor glycemic control in patients with diabetes for many years. Although HbA1c measurement is needed for calculating estimated average blood glucose (eAG), it is now recommended that eAG is used instead of HbA1c for expression of blood glucose control and communication with patients and health care providers. This study, investigated fasting blood glucose (FBS) as an indicator of overall chronic blood sugar control by assessing the correlation between FBS with eAG derived from HbA1c.
Methods: The blood samples for HbA1c assay were collected in EDTA tubes and were analyzed by an HPLC analyzer (G8 Tosoh, Japan). Blood samples for FBS were collected in serum separator tubes, transported, and centrifuged for 15 minutes at 3,000 g. FBS levels were determined in serum samples with the enzymatic hexokinase method by a clinical chemistry analyzer (Architect 8000, Abbott, USA).
Results: Statistical analysis was performed on 1,740 patients with type 2 diabetes mellitus with HbA1c levels above 6.5 mmol/L. The difference between FBS (9.3 ± 3.7 mmol/L) and eAG (11.14 ± 2.7 mmol/L) was statistically signif-icant (p < 0.0001). The correlation coefficient between FBS and eAG was r = 0.65 (95% CI; 0.62 - 0.69), with a p-value < 0.0001.
While the correlation coefficient between FBS and eAG at HbA1c < 6.5% was r = 0.251 (95% CI, 0.16 - 0.34), with a significant p-value of < 0.00001.
The combined data, standard deviation (SD), median, and interquartile range of eAG and FBS for all of the diabetic groups (n = 2,315), were 10.1 ± 3.00 mmol/L, 9.5 mmol/L, and 7.75 - 12.03 mmol/L for eAG, respectively. Similarly, these values were 8.5 ± 3.6 mmol/L, 7.5 mmol/L, and 6.0 - 10.00 mmol/L for FBS, respectively.
Conclusions: We concluded that there is a moderate and significant positive correlation between fasting blood sugar and the estimated average blood glucose derived from HbA1c. Although FBS might be helpful for daily monitoring of diabetes. Further studies must be conducted to provide solid results to support that FBS and its derived variable eAG can replace HbA1c as an indicator of long-term overall control of T2DM patients.

DOI: 10.7754/Clin.Lab.2020.200324