Abstract
It is impossible to measure insulin in the sera of insulin-treated patients by radioimmunoassay due to the presence of insulin antibodies in the sera. The same limitation appears to hold for enzyme immunoassay. However, the principle of the procedure in the Insulin Enzyme Immunoassay Kit (Mochida) is a sandwich method, although the radioimmunoassay depends on the competitive method. The binding capacity of insulin antibody in this enzyme immunoassay system thus appears to be still higher than that in the sera of insulin-treated patients. For this reason, the insulin antibodies in the sera of insulin-treated patients may be negligible compared to those in the assay system, and values obtained from the assay system for the sera of insulin-treated patients may be considered to express the total insulin values in the sera.
Measurements of insulin were carried out with this assay system for both sera and extracts of 18 insulin-treated subjects. Extraction of insulin was performed by the acid ethanol method. The values obtained for sera were compared with those for extracts, and were found to correspond closely. When the values for extracts were plotted on the X axis and those for sera on the Y axis, the following correlation between them was derived: Y=0.95X+ 42.12 (r= 0.951, p<0.001).
Fundamental examinations on the reproducibility, dilution test and recovery test, were performed with this assay system for sera containing insulin antibodies. The results were generally satisfactory.
It is concluded therefore that values obtained with this assay system for the sera of insulintreated patients, express the total serum insulin levels, even though insulin antibodies are present in the sera.
