Radioimmunoasay of calcitonin in plasma and cerebro-spinal fluid

An acceptable radioimmunoassay of calcitonin (CT) in man requires a highly purified antigen that can be labelled without loss of immunoreactivity. Radiolabelled synthetic CT showed an additional large peak of radiopeptides with high molecular weight. Therefore, a standard electrofocussing experiment was performed. Standards exhibiting an atypical behaviour after radioiodination showed a pI different from synthetic human monomer. CT electrophoretogram shows a larger component at pI 7.9 and two smaller contaminations at pI 8.6. Besides, the antisera available for CT assay are considered in healthy subjects. 0H2 and COOH assays give non-homogeneous results. A CT assay in cerebrospinal fluid is performed. The direct assay was unable to detect significant correlation between serum and cerebrospinal levels both in physiological and pathological conditions. Finally, the quality control of the CT assay is discussed. (Auth./G.J.P.)