False diagnosis of recurrent thyroid carcinoma: the importance of testing for heterophile antibodies.

Thyroglobulin (Tg) levels are important to predict recurrence in differentiated thyroid cancer patients.However, false-positive results can hence the request of unnecessary tests and treatments. We reported two cases of interference in thyroglobulin measurement and the workup to investigate them. Both patients achieved an excellent response to therapy after total thyroidectomy and one patient had also received radioiodine treatment. During the follow-up, Tg levels increased and there was no evidence of recurrent disease in the imaging studies. The Tg levels by the Access platform were positive but the results by Elecsys platform and LC-MS/MS were undetectable, leading to the hypothesis of heterophile antibodies (HAbs) interference. The possibility of HAbs interference must be considered when the Tg levels do not fit in the clinical picture. The measurement of Tg by another immunoassay or by LC-MS/MS may be useful in these situations.

The role of a new polyclonal competitive thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer with structural disease but low levels of serum thyroglobulin by immunometric and LC-MS/MS methods.

PURPOSE: The aims of this study were to assess the role of an in-house competitive thyroglobulin assay (Tg-c) in the follow-up of metastatic differentiated thyroid carcinoma (DTC) patients who presented underestimated Tg measurements by immunometric assays (Tg-IMA) and to compare the results with IMA and LC-MS/MS Tg methods. METHODS: This prospective study included 40 patients. Twenty-one with metastatic disease: 14 had Tg-IMA levels inappropriately low or undetectable (eight patients with positive and six with borderline TgAb) and seven had high Tg-IMA levels. Nineteen had an excellent response to therapy. The competitive assay employs a polyclonal antibody produced in rabbits immunized with human Tg, Tg labeled with biotin, and for the solid phase separation, a monoclonal anti-rabbit IgG antibody adsorbed to microtiter plates. RESULTS: All 14 patients with structural disease and underestimated levels of Tg-IMA presented detectable Tg-c levels. The median Tg-c level in the group with positive TgAb was 183 µg/L (range: 22-710 µg/L), and 58 µg/L (range 23-148 µg/L) in the borderline TgAb group. The levels of Tg-LC-MS/MS were detectable in some patients (range < 0.5-18 µg/L). All seven patients with high Tg-IMA presented also high levels of Tg-c. Only 2/19 patients with excellent response had Tg-c levels above the functional sensitivity. CONCLUSIONS: The competitive assay was able to detect Tg in all patients, even in the presence of serum TgAb, and may be an option in patients with underestimated Tg-IMA and relevant structural disease.

False diagnosis of recurrent thyroid carcinoma: the importance of testing for heterophile antibodies

SUMMARY Thyroglobulin (Tg) levels are important to predict recurrence in differentiated thyroid cancer patients. However, false-positive results can hence the request of unnecessary tests and treatments. We reported two cases of interference in thyroglobulin measurement and the workup to investigate them. Both patients achieved an excellent response to therapy after total thyroidectomy and one patient had also received radioiodine treatment. During the follow-up, Tg levels increased and there was no evidence of recurrent disease in the imaging studies. The Tg levels by the Access platform were positive but the results by Elecsys platform and LC-MS/MS were undetectable, leading to the hypothesis of heterophile antibodies (HAbs) interference. The possibility of HAbs interference must be considered when the Tg levels do not fit in the clinical picture. The measurement of Tg by another immunoassay or by LC-MS/MS may be useful in these situations.

Perfil epidemiológico de pacientes com diagnóstico de carcinoma diferenciado de tireoide em seguimento em ambulatório de endocrinologia / Epidemiological profile of patients diagnosed with differentiated thyroid carcinoma followed in an outpatient clinic of endocrinology

Objetivo: Avaliar o perfil epidemiológico de pacientes com diagnóstico de carcinoma diferenciado de tireoide. Métodos: Estudo analítico descritivo, realizado por meio da análise e da coleta de dados de 34 prontuários de pacientes em seguimento em um ambulatório de endocrinologia de um hospital público em São Paulo. Foram incluídos todos os pacientes em acompanhamento no ambulatório com diagnóstico de tumores diferenciados; foram excluídos os menores de 18 anos e/ou com diagnóstico de outras neoplasias de tireoide (que não tumores diferenciados). Resultados: A idade dos pacientes variou de 25 a 84 anos ao diagnóstico, com média de 51 anos, tendo sido representados por 32 mulheres (94,11%) e 2 homens (5,88%). A maioria dos tumores (41,17%) possuía tamanho entre 1 e 2cm. A maior parte dos pacientes tinha baixo risco de recorrência, e todos foram tratados cirurgicamente. Conclusão: O tumor diferenciado mais frequente é o subtipo papilífero. Sua prevalência se dá em mulheres, com média de idade ao diagnóstico de 51 anos. (AU)

Objective: To evaluate the epidemiological profile of patients with differentiated thyroid carcinoma. Methods: Th is i s a d escriptive, analytical study performed through the analysis and collection of data from 34 medical records of patients being followed in an endocrinology clinic of a public hospital in the city of São Paulo. All patients being followed at the outpatients' department with a diagnosis of differentiated thyroid carcinoma were included, and those under 18 and/or with diagnosis of other cancer of the thyroid (other than differentiated tumors) were excluded. Results: the patients' ages ranged from 25 to 84 years at diagnosis, an average of 51 years represented by 32 women (94.11%) and 2 men (5.88%). Most tumors (41.17 %) were between 1 and 2cm. Most patients showed low risk of recurrence, and all were surgically treated. Conclusion: The most frequent differentiated tumor was the papillary one. Its prevalence was on women, with an average age at diagnosis of 51 years. There were only two patients with recurrent disease, and one with metastasis to the lung that died. (AU)