Radioimmunoassay of serum thyroglobulin. Technique and clinical results.

A radioimmunoassay technique using a double antibody procedure for human serum thyroglobulin (HTg) is described. Only antigen labeling with iodine-125 is performed extemporaneously, the other reagents being purchased commercially. Quality criteria were: sensitivity (2 microgram/l), interassay reproducibility (coefficient of variance, C.V. = 11%) and specificity are comparable with those of previously published techniques. Normal limits for serum HTg concentrations were established on the basis of 65 assays (33.0 +/- 21.20 microgram/l). In 69 subjects exhibiting goiters and cold nodules, the values observed were considerably higher and more dispersed (81 +/- 57 microgram/l); the same observation was made for the the cases of Basedow's disease studied. Patients who had undergone thyroid ablation for thyroid cancer exhibited a low or nondemonstrable HTg concentration, except for seven subjects showing osseous and/or pulmonary functionally active metastases of a differentiated cancer whose HTg levels were significantly higher (300-400 microgram/l). These results concur with several previous reports in emphasizing the interest of assaying serum HTg during the surveillance of differentiated cancers of the thyroid.