[Serum thyroglobulin and whole-body scanning as markers in the follow-up of differentiated thyroid carcinomas]

We have compared two "markers" in the follow up of post treatment (surgery and therapeutical use of I-131) differentiated thyroid carcinoma. In 153 patients, thyroglobulin (Tg) serum levels were measured after withdrawal of I-thyroxine therapy, before performing a whole-body scan (WBS) with iodine-131; in 55 of these patients, Tg was measured again after at least 45 days of I-thyroxine treatment. The patients were followed between 3 and 10 years, and there were 2713 matched studies. Our results indicate for both parameters, false positive and negative values; sensitivity (SE) for WBS was 89% and specificity (SP) 83%; Tg presents a SE of 86% and SP of 83%. Matching both parameters, SE was 95% and SP 98%. The causes of false results are discussed. Tg determinations under I-thyroxine treatment do not permit the establishment of absence of illness; 37.7% of patients with demonstrated metastases or relapse showed negative Tg values that reached pathological values after suspension of I-thyroxine treatment; another 41.4% with elevated Tg values under therapy reached these values after suspension of I-thyroxine. Both markers, when utilized at the same time, offer the best possibilities in the follow-up of differentiated thyroid carcinoma, when determinations are carried out after suspension of hormonal treatment.