This study demonstrated the efficacy of low doses in patients with lower remnants after surgery (uptake <2%), the inverse correlation between uptake and ablation efficacy with low and high doses, and the usefulness of the measurement of cervical uptake for the definition of the ablative 131I dose.

Posttherapy scanning provides important information, even in patients whose pretherapy WBS is positive for metastases, with this approach being useful both during the first ablation and subsequent treatment.

Objective. To determine the sensitivity of thyroglobulin (Tg), iodine scanning, and sonography in the diagnosis of cervical recurrence of thyroid cancer. Methods. This prospective study assessed 81 patients with cervical metastases or extrathyroid invasion at first appearance who underwent clinical examination, scanning, measurement of Tg after thyroxine withdrawal, and sonography about 8 months after thyroidectomy followed by radioiodine treatment. Only patients without distant metastases and without anti‐Tg antibodies were included. Results. Fifty patients showed persistence of the disease in the cervical region, with only 16% of them having had a suspicion on clinical examination, 33 with Tg levels of 2 ng/mL or greater (66% sensitivity), and 29 with positive scan findings (58% sensitivity). A combination of the 2 methods detected disease in 40 (80%) of 50 patients but failed to show 20% of cases that were identified by sonography and confirmed by fine‐needle aspiration. Sonography had sensitivity of 96%. Specificity values for Tg, iodine scanning, and sonography were 80.6%, 90.3%, and 87%, respectively. Conclusions. Classic follow‐up methods may not detect cervical disease in some patients with differentiated thyroid carcinoma, and sonography is necessary even in patients apparently free of the disease.

Undetectable Tg on T4 combined with negative neck US presented a high NPV in low-risk patients and Tg stimulation might be avoided in these patients.

Radioiodine causes transitory alterations in ovarian function even in younger women and after a mean activity of 4.2 GBq (115 mCi).

Antithyroglobulin antibodies (TgAb) were measured using a chemiluminescent immunoassay (ICMA) and an agglutination test. TgAb laboratory and clinical interference with Tg measurements were assessed. The course of TgAb concentration and disease status were compared during 3 years after initial treatment. The agglutination test failed to detect all titers < 10IU/mL (ICMA). Interference from TgAb was common at high titers, but even low antibody titers (< 5IU/mL) were able to interfere with Tg measurement. Cases of distant metastases with undetectable Tg (by IRMA) and those apparently free of disease and without thyroid remnants with Tg> 2ng/ml (by RIA) were identified among patients with TgAb. The exogenous Tg recovery test was normal (> 80%) by the two methods in 22% of patients with TgAb and confirmed laboratory interference. Absence of reduction in TgAb levels was a marker of persistent disease. In conclusion, TgAb should be determined by immunoassays; interference with Tg measurements occurred mainly but not always at high concentrations, with a normal Tg recovery test not excluding this interference. The behavior of TgAb is related to disease persistence or cure. Anticorpos anti-tireoglobulina (TgAb) foram medidos por um imunoensaio de quimioluminescência (ICMA) e um teste de aglutinação. Avaliamos a interferência clínica e laboratorial dos TgAb com as medidas de Tg. A evolução da concentração dos TgAb e o estado da doença foram comparados durante 3 anos após o início do tratamento. O teste de aglutinação falhou em detectar todos o títulos <10UI/mL (ICMA). Interferência dos TgAb foi comum com títulos altos, mas mesmo títulos baixos dos anticorpos (<5UI/mL) interferiram na medida de Tg. Casos com metástases à distância e Tg indetectável (por IRMA) e aqueles aparentemente livres da doença e sem remanescentes tireoidenos com Tg >2ng/ml (por RIA) foram identificados entre pacientes com TgAb. O teste de recuperação da Tg exógena foi normal (>80%) por ambos os métodos em 22% dos pacientes com TgAb, confirmando a interferência laboratorial. Ausência de redução dos níveis de TgAb foi um marcador de persistência da doença. Em conclusão, TgAb deve ser determinada por imunoensaios; interferência com as medidas de Tg ocorreram principalmente mas não somente em altas concentrações, com um teste normal de recuperação de Tg não excluindo esta interferência. O comportamento dos TgAb está relacionado à persistência ou à cura da doença.

No abstract

Postoperative Tg less than 10 ng/mL rarely show distant metastases and because these metastases were observed in 31% of patients with values greater than 10 ng/mL, this criterion can be selected for the indication of imaging methods, in addition to neck ultrasound (US). For cases with Tg less than 10 ng/mL, US is necessary because even patients with undetectable Tg had lymph node metastases. The same cut-off can be used for the indication of radioiodine therapy even in the absence of any evidence of disease because 51% of the patients with Tg greater than 10 ng/mL showed ectopic uptake on posttreatment scanning.