ANNALS EXPRESS: Establishment of glycated albumin unit conversion equation from the standardized value (mmol/mol) to the routinely used value (%).

Background To promote glycated albumin (GA) standardization, Committee on Diabetes Mellitus Indices, Japan Society of Clinical Chemistry published the recommended reference method, and is supplying the reference standard material (JCCRM 611). In this study, we evaluated the basic performance of "standardized enzymatic method" that is traceable to JCCRM 611, and established a unit conversion formula from standardized GA value (mmol/mol) to the routinely used GA value (%) . Methods To evaluate accuracy and within-run reproducibility of the "standardized enzymatic method", JCCRM 611 was measured 20 times. To establish the unit conversion formula, serum specimens with known HbA1c levels were collected, and their GA (%) and GA (mmol/mol) were measured. Results The accuracy of GA value of the "standardized enzymatic method" was 100.8-103.0%. The within-run reproducibility CV (coefficient of variation, %) of GA value was 0.6-0.9%. In total, 240 serum specimens were collected and the distribution of their HbA1c values were HbA1c ≤ 4.9% (n = 23), 5.0-5.9% (n = 50), 6.0-6.9%, (n = 44), 7.0-7.9% (n = 40), 8.0-8.9% (n = 37), and ≥ 9.0% (n = 46). The unit conversion equation was defined as: GA (%) ＝ 0.05652  GA (mmol/mol) - 0.4217 (r = 0.999). GA (%) calculated by the equation was in close agreement (96.6-104.2%) with the actual measured GA (%). Conclusions The GA unit conversion formula was established from mmol/mol to %. This formula provides an easy method to convert the unit, and is expected to be useful for the standardization of GA measurement. Key words: Glycated albumin, standardization, unit conversion formula.