Patent ID: 7855079

Claim:
A method for directly assaying percentage of glycated hemoglobin A1c in a blood sample without measuring the total hemoglobin in the blood sample in a separate process, said method comprising: a) contacting protein fragments containing glycated peptides or glycated amino acids with a fructosyl amino acid oxidase to generate hydrogen peroxide (H 2 O 2 ), wherein the protein fragments are generated by contacting the blood sample with 1) a lysing buffer which releases hemoglobin from red blood cells in the blood sample; 2) an oxidizing agent which is a tetrazolium salt, and 3) a protease which digests glycated hemoglobin into glycated peptides or glycated amino acids, wherein the protease is a neutral protease of Aspergillus or Bacillus origin and generates glycated glycine, glycated valine, glycated lysine residue, or a glycated peptide comprising glycated glycine, glycated valine or glycated lysine residue; wherein the fructosyl amino acid oxidase comprises the amino acid sequence set forth in SEQ ID NO:1; b) contacting H 2 O 2 generated in step a) with a color forming substance in the presence of a peroxidase to generate a measurable signal; and c) determining percentage of glycated hemoglobin A1c by correlating the measured value in step b) to a percentage of glycated hemoglobin A1c in a calibration curve without measuring the total hemoglobin in the blood sample separately.