Simple colorimetry of glycated serum protein in a centrifugal analyzer

A recently described (Clin Chim Acta 127: 87-95, 1982) colorimetric assay for glycated proteins in serum exploits their ketoamine activity to reduce 3,3'-(3,3'-dimethoxy-4,4'-biphenylylene)bis [2-(p-nitrophenyl)-5-phenyl-2H-tetrazolium chloride] (nitroblue tetrazolium) in alkaline solution; the authors termed this the "fructosamine assay." The method is simple, requiring only the addition of one reagent and measurement of the absorbance change during 5 min; results are expressed relative to a synthetic standard. We have adapted this for use in a centrifugal analyzer and report its performance, both analytically and as an index of hyperglycemia. Precision is good (between-batch CV 2.1%), the reagent is stable and inexpensive, and the procedure is rapid (75 samples per hour). Albumin influences the measurement, but for concentrations greater than or equal to 35 g/L this was not a serious problem. Normal and diabetic populations can be clearly discriminated (p less than 0.001). The test detected 25 (84%) of the 30 untreated diabetics studied and gave four false positives (8%). The results correlate well with those for glucose in plasma of fasting subjects (r = 0.87) and for hemoglobin A1 (r = 0.80).