[Radioimmunoassay for the determination of glycated hemoglobin and its clinical significance].

The glycosylated hemoglobin (Hb) is a useful marker for monitoring blood glucose concentrations over the prior one or two month period. A variety of method has been described for the determination of glycated Hb, but many of them have serious pitfalls. In this report, a radioimmunoassay for glycated Hb was developed and its clinical significance was described. The antiserum was obtained by immunizing guinea pigs with reduced glycated human serum albumin. This antiserum was capable of identifying glucitollysine residues on glycated Hb of normal and diabetic individuals after reduction with NaBH4. The RIA described here had satisfactory reproducibility as judged by the intra-assay (1.6-3.7%) and inter-assay (1.7-5.4%) precision. To evaluate the usefulness of this RIA method, HbAlc values measured by HPLC method were compared with values by this RIA method. According to the criteria of the WHO Expert Committee on Diabetes Mellitus, 80 subjects were divided into normal group (N), impaired glucose tolerance group (IGT), and diabetic group(DM). Average of glycated Hb values obtained by this RIA in 20 IGT subjects was significantly higher (p less than 0.001) than that of 30 normals and 17 IGT subjects exceeded upper normal range (mean + 2SD). But there was no significant difference between N and IGT in the levels of HbAlc by HPLC and all IGT subjects remained normal range. In a patient treated with continuous subcutaneous insulin infusion therapy failure of normalization of the glucose balance was discernible by an elevation of glycated Hb values by RIA. In contrast, HbAlc values fell within the normal range in this patient. From these results it appears that determination of glycated Hb by this RIA represents a more sensitive parameter for long-term than HbAlc by HPLC and is suitable for monitoring even small fluctuation of blood glucose.