Development of hemoglobin A1c certified reference material by liquid chromatography isotope dilution mass spectrometry

We report the development of a National Institute of Metrology (NIM) hemoglobin A_1c (HbA_1c) certified reference material (CRM). Each CRM unit contains about 10 μL of hemoglobin. Both hemoglobin and glycated hemoglobin were quantitatively determined by high-performance liquid chromatography (HPLC)–isotope dilution mass spectrometry (IDMS) with synthesized VHLTPE and glycated VHLTPE as standards. The mass fraction of synthesized VHLTPE or glycated VHLTPE was also quantitatively determined by HPLC-IDMS with NIM amino acid CRMs as standards. The homogeneity and stability of the CRMs were examined with a commercial HbA_1c analyzer based on the HPLC principle. Fifteen units were randomly selected for homogeneity examination, and statistical analysis showed there was no inhomogeneity. Examination of the stability showed that the CRM was stable for at least 6 months at -80 °C. Uncertainty components of the balance, amino acid purity, hydrolysis and proteolysis efficiency, method reproducibility, homogeneity, and stability were taken into consideration for uncertainty evaluation. The certified value of NIM HbA_1c CRM was expressed as the ratio of HbA_1c to total hemoglobin in moles, and was (9.6 ± 1.9)% . The CRM can be used as a calibration or validation standard for clinical diagnostics. It is expected to improve the comparability for HbA_1c measurement in China.