title: Challenges in interpretation of thyroid hormone test results.
abstract: BACKGROUND
  In interpreting thyroid hormones results it is preferable to think of interference and changes in concentration of their carrier proteins.
  
  
  METHODS
  We present two patients with discrepancy between the results of thyroid function tests and clinical status. The first case presents a 62-year-old patient with a nodular goiter and Hashimoto thyroiditis. Thyroid function test showed low thyroid-stimulating hormone (TSH) and normal to low fT4. By determining thyroid status (TSH, T4, fT4,T3, fT3) in two laboratories, basal and after dilution, as well as thyroxine-binding globulin (TBG), it was concluded that the thyroid hormone levels were normal. The results were influenced by heterophile antibodies leading to a false lower TSH level and suspected secondary hypothyroidism.The second case, a 40-year-old patient, was examined and followed because of the variable size thyroid nodule and initially borderline elevated TSH, after which thyroid status showed low level of total thyroid hormones and normal TSH. Based on additional analysis it was concluded that low T4 and T3 were a result of low TBG. It is a hereditary genetic disorder with no clinical significance.
  
  
  CONCLUSIONS
  Erroneous diagnosis of thyroid disorders and potentially harmful treatment could be avoided by proving the interference or TBG deficiency whenever there is a discrepancy between the thyroid function results and the clinical picture.
authors.forename: Tijana
authors.initials: T
authors.lastname: Lalić
authors.forename: Biljana
authors.initials: B
authors.lastname: Beleslin
authors.forename: Slavica
authors.initials: S
authors.lastname: Savić
authors.forename: Mirjana
authors.initials: M
authors.lastname: Stojković
authors.forename: Jasmina
authors.initials: J
authors.lastname: Cirić
authors.forename: Milos
authors.initials: M
authors.lastname: Zarković
mesh_terms: D000328:Adult; D000910:Antibodies, Heterophile / Q000097:blood*; D005260:Female; D040181:Genetic Diseases, X-Linked / Q000097:blood*; D006044:Goiter, Nodular / Q000097:blood*; D050031:Hashimoto Disease / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013960:Thyroid Function Tests / Q000379:methods*; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D056825:Thyroxine-Binding Globulin / Q000172:deficiency* / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood
chemical_list: D000910:Antibodies, Heterophile; D013963:Thyroid Hormones; D056825:Thyroxine-Binding Globulin; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine