Re-examination of human calcitonin radioimmunoassay

Evaluations of human immunoreactive calcitonin (IRCT) assay have been extensively reviewed. Labelled hormone was re-purified on carboxymethyl-cellulose in order to isolate a fraction containing mainly monoiodinated calcitonin, which was found to be very stable. Two antisera with different immunochemical characteristics were used for incubation studies, one of which was incubated with unextracted and extracted plasma samples. The sensitivity of the assays was 60 pg/ml plasma. However, marked differences were observed in the results obtained by the three methods depending on the importance of the inhibitory effect of plasma on the binding of the tracer to antibodies. However, the absolute plasma IRCT level could not be related to the presence of calcitonin M, except in one case. Further studies are needed in order to ascertain the origin and the significance of the immunoreactive material which was detected in normal plasma by one antiserum.