ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P754

Interference in assay of thyroid hormones due to auto-antibodies against thyroxine and triiodothyronine: report on two patients with Hashimoto's thyroiditis

Oscar Moreno-Pérez1, Joaquin Serrano1, Rocio Alfayate2, Maite López2, Sandra Martinez-Fuster1, Nieves Arias1, Monsrrat Mauri2 & Antonio Miguel Picó1

1Department of Endocrinology and Nutrition, Alicante General University Hospital, Alicante, Spain; 2Department of Hormone Laboratory, Alicante General University Hospital, Alicante, Spain.

Introduction: Characteristically the discordant thyroid function test has been attributed to TSH-producing hypophyseal adenoma, familial dysalbuminemic hyperthyroxinemia and thyroid hormone resistance syndrome. We presented 2 cases with raised peripheral thyroid hormones with detectable TSH due to the presence of auto-antibodies against the peripheral thyroid hormones (PTAAb).

nv0.38–4.84 μU/ml0.8–2 ng/dl0.7–1.48 ng/dl<1.6%1.8–4.6 pg/ml1.71–3.71 pg/ml<2%0–0.9 mU/ml11–124 nmol/l

Subjects and methods: A 24-year-old woman (1) and a 79-year-old woman (2) with auto-immune primary hypothyroidism diagnosed 4 and 3 years ago, with symptoms and signs of clinical hypothyroidism and without levothyroxine treatment was referred to our centre after a finding of discordant thyroid function values (Table). Hormonal and radioimmunoprecipitation studies. Subunit-α was determined by IRMA (Immunotech de Beckman Coulter©), SHBG by QLA (Immulite 2000 (DPC©), TSH was determined by EQLA, following series dilution (1/2, 1/5) of the sample. Samples were sent to another laboratory for determination of TP by ‘two-step’ immunoassay (CMIA, Architect (Abbott Lab©). TPAAb was determined by incubating samples with I125-T4 and I125-T3, followed by precipitation in polyethylene–glycol. Precipitate count was obtained using a gamma-counter (Packard Cobra). Euthyroid patients with no auto-immune pathology were used as controls.

Results: The presence of PTAAb was detected in both cases (table), confirming the initial diagnosis of primary hypothyroidism.

Conclusion: The presence of PTAAb is an unusual cause of discordant thyroid function values that it must have in mind to the correct management of thyroid disease.