Hemoglobin A1c determination in the A1C-Derived Average Glucose (ADAG) study

The A1C-Derived Average Glucose (ADAG) study was commenced to gain a better understanding of the relationship between HbA1c and average blood glucose and to investigate if HbA1c could be expressed in the same units as day-to-day glucose monitoring. Owing to the impact of the outcome of this study it was very important to determine HbA1c values with a minimum of uncertainty and as close as possible to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) primary reference method, which is the only valid anchor of HbA1c standardization. Approximately 2300 samples were analyzed with four IFCC secondary reference methods. Additional off-line calibration with IFCC secondary reference material with assigned IFCC values was performed to improve the uncertainty in the HbA1c value determination. Additional off-line calibration improved the 95% confidence interval between the four different HbA1c methods at HbA1c of 6.00% from +/-0.28% (5.72%-6.28%) to +/-0.20% (5.80%-6.20%) and at HbA(1c) of 9.00% from +/-0.43% (8.57%-9.43%) to +/-0.24% (8.76%-9.24%). The HbA1c results used in the ADAG study were determined with the lowest uncertainty technically feasible by using four certified IFCC secondary reference methods and additional off-line calibration with IFCC secondary reference material.