Abstract
In the two-antibody assay system for insulin, insulin-free human plasma and human globulin fraction reduced the percentage of precipitated insulin-131I Insulin antibody in plasma was partially absorbed by means of anti-human globulin rabbit serum, which was not available for the removal of endogenous insulin antibody. In order to remove the inhibiting factor as well as the circulating insulin antibody, a simple method for the extraction of plasma insulin was described. The method consists of extraction by acid-ethanol and precipitation in cold acetone. The recovery rate of insulin-131I added to serum by the present method was 92%, and that of human insulin added to a pooled human plasma was in the range of 80 to 94%. The extract contained a small amount of albumin but not globulin. The extraction method completely separated the insulin from the insulin-antibody complex.
The mean values of the fasting extractable insulin in human plasma were 20.5, 19.3, 22.6 and 10.0μU per ml in normal subjects, mild, moderate and severe diabetic patients, respectively. In the latter group the insulin response to glucose load decreased. Extractable insulin in plasma of several diabetic patients with insulin antibody was, found to be 10 to 32μU per ml. The insulin level in plasma of insulin-dependent patient with antibody to insulin could be estimated by the present extraction method.
