Improved colorimetric assay for glycosylated hemoglobin

This colorimetric assay for glycosylated hemoglobin can be performed in 120 min with equipment available in most clinical laboratories. The glucose moiety of glycosylated hemoglobin is converted to 5-hydroxymethylfurfural by heating with oxalic acid for 60 min is an autoclave at 124 degrees C and 124 kPa (18 lb/in.2). The adduct formed by reacting 2-thiobarbituric acid with hydroxymethylfurfural is measured photometrically and results are expressed either as nanomoles of hydroxymethylfurfural or as fructose equivalents. Within-assay and between-assay coefficients of variation were less than 2% and less than 3%, respectively. Comparison of results for 50 patients' specimens as measured by the present assay and as analyzed for hemoglobin A1c by liquid chromatography showed excellent correlation (r = 0.98).