A convenient assay of glycoserum by nitroblue tetrazolium with iodoacetamide.

BACKGROUND To determine glycoserum, the nitroblue tetrazolium (NBT) assay is quick, economical, convenient and easily automated. This method, however, is vulnerable to interference by thiol group, which should not be ignored during the analysis. METHODS Thiol group in glycoserum was blocked with iodoacetamide (IAM) before NBT was added. The reaction was carried out in a thermal bath and terminated on ice. The absorbance was measured at either 570 or 530 nm. RESULTS IAM (3-10 mmol/l) did not give any detectable interference in the NBT assay. The absorbance at both 570 and 530 nm was linearly related to the concentration of either glycoserum or 1-deoxy-1-morpholino-D-fructose (DMF) that had been treated with IAM. The assay showed a good discrimination between diabetic and normal subjects (t-test, P < 0.001). Uric acid and lipemia under physiological conditions did not interfere with NBT reaction. The assay was affected by hyperlipemia and hematolysis. CONCLUSIONS IAM-modified method prevented NBT assay from the interference by thiol group and uric acid.