Radioimmunoassay of human calcitonin using labeled [Asu1, 7]-human calcitonin analogue.

Application of synthetic human calcitonin analogue ([Asul,7]-hCT) was attempted, since it is chemically more stable than native hCT. [Asu1, 7]-hCT was successfully labeled with 125I to a specific activity ranging from 410 to 540 microCi/microgram. Sensitivity, recovery and reproducibility of the assay system using 125I-labeled [Asu1,7]-hCT analogue, standard synthetic hCT and its antibodies, were 49 pg/ml, 99.8 +/- 4%, and 7.95% (C. V. within assay) or 21.9% (C. V. between assays), respectively. The dilution curve of the sera obtained from patients with medullary carcinoma paralled well with the standard curve. 125-I-labeled [Asu1, 7]-hCT analogue can be used for routine radioimmunoassay of hCT.