Abstract: RADIOIMMUNOASSAY FOR THYROCALCITONIN IN SERUMSu Jingxian\ Han Shiquan\ Hou Yue\ Liu Yibing\ Chen Jian\ Hou Huiren(Department of Isotope, China Institute of Atomic Energy, Beijing 102413)ABSTRACTA specific radioimmunoassay(RIA) for thyrocalcitonin(CT) is developed and applied to the measurment of serum. CT is iodinated according to the method of chT and purified by Sephadex G50. The specific activity of 125ICTB more than 9.5 TBq/g，the radiochemical purity is more than 95% and the excessive antibody binding is (85-91)%. The kit has a stable lyophilization standards. The range of detection is 8.8-351 pmol/L. This method is simple and fast. The average recovery in serum is (95.5-102.0)%.The intra and inter coefficients of variation are (3.2-8.6)% and (4.7-10.4)%,respectively. The nonspecific binding is (2.4-4.7)%,the sensitivity is 5.3 pmol/L and the correlation coefficient of high value serum dilution is 0.999 3-0.999 8.The content of CT in 82 healthy adults is 11.7±6.4 pmol/L.Key words thyrocalcitonin(CT)\ radioimmunoassay(RIA) labeling of 125I