Radioimmunoassay for serum thyroglobulin designed for early detection of metastases and recurrencies in the follow-up of patients with differentiated thyroid carcinoma.

A radioimmunoassay (RIA) for the measurement of thyroglobulin in human serum was developed and factors that influence sensitivity were investigated. In a comparison of 3 different labeling procedures (chloramine T, iodogen, lactoperoxidase) iodogen-prepared tracer proved to be slightly superior with respect to sensitivity and stability. The shelf life of the tracer was improved by a protein-enriched buffer, which serves as a radical scavenger. The binding kinetics of tracer to antibody at different temperature ranges were examined, and the most rapid and complete binding was found at room temperature. For the preparation of standard curves, several artificial media were compared with thyroglobulin-free serum. Second antibody separation was investigated and optimized. By employing sequential saturation, sensitivity of 0.75 microgram/1 (B0-3 SD) and 50% intercept of less than 5 micrograms/l were achieved. The results of RIA measurements of thyroglobulin in 142 patients with papillary and follicular thyroid carcinoma after thyroidectomy and 131I treatment were compared with 131I whole-body scans. The results confirmed that serum thyroglobulin is an early indicator of recurrency.