Comparative Study of Estimated Fasting Plasma Glucose from HbA1c Among Six Hospitals

Witchuda Pongthong, Abhiwutta Kongkird, Jindarat Trakulthong, Wisut Kangwantrakul, Limthong Promdee


This study aimed to compare the estimated fasting plasma glucose (eFPG) from HbA1c using the formula recommended by the American Diabetes Association (ADA); estimated average glucose, eAG (mg/dL) = (28.7 x HbA1c) - 46.7, and the formula derived from own FPG and HbA1c within 6 hospitals.  With the use of ADA formula, eFPG was higher and significantly different from FPG in all 6 hospitals (r = 0.4 – 0.5, p< 0.05).  Five of  the six hospitals showed eFPG higher than FPG±10%, and 72% of diabetic patients had lower blood glucose level when compared with eFPG calculated from ADA formula.  The ADA-recommended formula was calculated based on capillary blood glucose level determined by glucometer, while in Thai diabetic patients, fasting plasma glucose was performed on automated analyzer.  Therefore, we calculated eFPG based on own FPG and HbA1c values of each hospital.  The results showed significant correlation between eFPG and FPG (r = 0.3 - 0.7, p < 0.05).  Four of  the six hospitals showed eFPG  fell within ±10% of FPG.  The number of  lower fasting blood glucose level when compared with eFPG was reduced to 49%. Thus eFPG should be estimated from formula derived from own data of each hospital to provide better assessment of glycemic control of its patients.

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