Method of quantifying glycosylated protein using redox reaction and quantification kit

A method of measuring the amount of a glycated protein present in a sample, comprising:

• pretreating said sample by adding an amount of a reagent containing a degradation a fructosyl amino acid oxidase (degradation FAOD) so that a glycated free amino acid that is present in the sample as a contaminant is degraded by the by the action of said degradation FAOD and the glycated protein remains in the sample;
• adding an amount of a protease reagent containing a protease to the sample to degrade said glycated protein remained in the sample and produce a degradation product of the glycated protein;
• adding an amount of a reagent comprising a measurement a fructosyl amino acid oxidase (measurement FAOD) to the sample after adding said protease reagent to cause a redox reaction between the measurement FAOD and the degradation product of the glycated protein and to generate hydrogen peroxide;
• and
• wherein the redox reaction is conducted in the presence of a solution containing a combination of a tetrazolium compound and sodium azide, said combination of tetrazolium compound and sodium azide being added to the sample at the same time with the protease;
• measuring the amount of hydrogen peroxide generated by the redox reaction to determine the amount of the glycated protein present in the sample,
• wherein the measurement of the amount of hydrogen peroxide comprises
• adding a color-developing substrate to allow a redox reaction between the color-developing substrate and the hydrogen peroxide generated, and
• measuring an amount of color developed by the color-developing substrate to determine the amount of the hydrogen peroxide.