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

Abstract

Background: To promote glycated albumin standardization, the 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 glycated albumin value (mmol/mol) to the routinely used glycated albumin value (%). Methods: To evaluate the 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 concentrations were collected, and their glycated albumin (%) and glycated albumin (mmol/mol) were measured. Results: The accuracy of glycated albumin value of the ‘standardized enzymatic method’ was 100.8–103.0%. The within-run reproducibility CV (coefficient of variation, %) of glycated albumin value was 0.6–0.9%. In total, 240 serum specimens were collected, and the distribution of their HbA1c values was 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). Glycated albumin (%) calculated by the equation was in close agreement (96.6–104.2%) with the actual measured glycated albumin (%). Conclusions: The glycated albumin 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 glycated albumin measurement.