Interlaboratory comparison of radioimmunological calcitonin determination

An interlaboratory study for the radioimmunological determination of calcitonin was performed within the European PTH Study Group (ESPG), to improve comparability using external quality control. Twelve laboratories determined calcitonin in 21 deep frozen samples using their respective calcitonin radioimmunoassay systems. The samples included a standard curves of human calcitonin (sequence 1-32) in serum as well as in assay buffer, several dilutions of a serum from a patient with medullary thyroid carcinoma, and additional sera containing calcitonin levels of clinical importance. For evaluation, the known concentrations were related to the measured values of each laboratory, and of all laboratories together. Except for one, the laboratories recognized the different dilutions used, although absolute values were scattered over a wide range. Satisfactory agreement was reached only when the data were calculated as the percentage of a given value. In future, a serum with a well defined and constant calcitonin concentration should be used as an international standard in all determination of calcitonin by radioimmunoassay.