False hyperthyroidism caused by interference in immunoassays

Clara Jiménez García; Piedad Ortega Fernández; María Eugenia Torregrosa Quesada; Victoria González Bueno; María Teresa Botella Belda; Rocío Alfayate Guerra

doi:10.1515/almed-2020-0097

False hyperthyroidism caused by interference in immunoassays

Adv Lab Med. 2020 Nov 13;2(1):121-128. doi: 10.1515/almed-2020-0097. eCollection 2021 Mar.

[Article in English, Spanish]

Authors

Clara Jiménez García¹, Piedad Ortega Fernández², María Eugenia Torregrosa Quesada¹, Victoria González Bueno¹, María Teresa Botella Belda¹, Rocío Alfayate Guerra¹

Affiliations

¹ Laboratory of Hormones, Hospital General Universitario de Alicante, Pintor Baeza 11, Alicante, Spain.
² Laboratory of Clinical Chemistry, Hospital General Universitario de Elche, Almazara, Elche, Spain.

Abstract

Objectives: Immunoassays used to assess thyroid function are vulnerable to different types of interference that may affect clinical decision-making.

Case presentation: We report the case of a 37-year-old woman who developed iatrogenic hypothyroidism after having received radioiode therapy who visited our hospital for her annual checkup. The patient was asymptomatic, without signs suggestive of thyroid disease. However, laboratory analysis proved otherwise: thyrotropin (TSH) 7.75 mU/L, thyroxine (FT4) >7.7 ng/dL.

Conclusions: The inconsistency between her clinical symptoms and the biochemistry data raised the possibility of a methodological interference. A thorough evaluation of the main causes of interference was conducted in the laboratory to exclude the presence of interference in TSH and FT4. Finally, different interfering agents were identified, which affected free thyroid hormone and TSH determination.

Keywords: heterophilic antibodies; hyperthyroidism; interference of immunoassay.