Hemoglobin A1c (HbA1c) levels in whole blood samples are commonly used to diagnose diabetes and monitor the effectiveness of glycemic control. However, there have not been many studies evaluating changes in HbA1c concentration under different storage conditions and analytical methods. The purpose of this study was to evaluate the stability of %HbA1c stored at different temperature conditions using immunoassays in order to improve the quality of HbA1c test. Whole blood samples collected from 10 healthy volunteers were anticoagulated with K2 EDTA and stored at the following temperatures: 20-25°C, 2-8°C, and -20°C. %HbA1c in human whole blood samples at each time point was determined simultaneously on Standard F Analyzer (%HbA1c-S) with reagent kit based on a reflectometry and immunoassay technology, and Erba XL640 system (%HbA1c-E) used immunoturbidimetric method, respectively. %HbA1c was assessed as stable when the difference in HbA1c level at the later time point was not statistically significant (p >0.05) compared with baseline (T0). Results showed that a positive correlation between %HbA1c-S and %HbA1c-E at T0 (r=0.9996) was observed at room temperature. %HbA1c-S was stabilized for 24 hours at 20-25°C, for 2 days at 2-8°C and for more than 1 month at -20°C. %HbA1c-E was stable for 12 hours at 20-25°C; less than 1 day at 2-8°C, and less than 1 month at -20°C. In conclusion, human whole blood samples for HbA1c determination can be stored for up to 1 month at -20°C.

Background: The research aimed to increase certain HbA1c concentrations at medical decision levels for external quality control samples from healthy donor blood.

Methods: The in vitro study was performed from October 2019 to January 2021 at Quality Control Center for Medical Laboratory at University of Medicine and Pharmacy at Ho Chi Minh City. The study observed on the conditions including the optimal buffer solutions (BAGPM, BPS, Ringer, Saline), temperature (2ºC - 8ºC, 22ºC - 24ºC, 37ºC), and glucose concentration (100 mM, 305 mM, 500 mM) affecting the HbA1c concentration in vitro to make the external quality control samples fell in normal, prediabetes, and diabetes range. At every condition, the HbA1c concentration was measured by Tina Quant method to look for the optimal procedure to increase HbA1c concentration required of the external quality control protocol.

Results: The highest HbA1c concentration (11.57±0.2%) was found in BAGPM solution with 100 mM glucose after 15 days with the baseline HbA1c 5.43±0.13%; the HbA1c level increase dramatically at 37ºC in BAGPM 500 mM glucose solution in fifteen days (40.03±1.05%).

Conclusions: The appropriate conditions were identified to prepare HbA1c standards for prediabetic and diabetic levels. The standards for HbA1c concentrations were recommended to prepare by incubating RBCs from non-diabetic donor blood in BAGPM solution containing glucose at 37ºC for 24 hours. Glucose concentrations should be 100 mM and 500 mM, respectively, for prediabetic level (HbA1c ~ 6.0 ± 0.12%) and diabetic level (HbA1c ~ 9.6 ± 0.17%).