title: Diagnostic confusion attributable to spurious elevation of both total thyroid hormone and thyroid hormone uptake measurements in the setting of autoantibodies: case report and review of related literature.
abstract: OBJECTIVE
  To review the effect of thyroid autoantibodies on thyroid function assays and to present a case in which thyroid autoantibodies resulted in spurious assay readings for both total thyroid hormone levels and thyroid hormone uptake measurements.
  
  
  METHODS
  We present a detailed case, including serial laboratory data, and review the relevant literature.
  
  
  RESULTS
  A 61-year-old man with a history of autoimmune disease presented for evaluation of abnormal results of thyroid function tests. The patient had been treated for hypothyroidism with levothyroxine and was noted to have an elevated total thyroxine (T4) level in the setting of a low total triiodothyronine (T3) value and a mildly elevated thyrotropin concentration. He had been referred for evaluation of a presumed deiodinase deficiency that impaired conversion of T4 to T3. During treatment with levothyroxine, these test results were confirmed, and the patient was also found to have an elevated T4 uptake. These findings were initially thought to be due to an excess of transthyretin; however, more extensive testing revealed that the patient had an autoantibody to T4 that interfered with the assays for both T4 and T4 uptake.
  
  
  CONCLUSIONS
  Autoantibodies to both T3 and T4 have been described. Such antibodies are not uncommon in patients with thyroid disease. On rare occasions, these antibodies may cause spurious assay readings and obscure the diagnosis. To our knowledge, this is the first report in which both the total T4 level and the T4 uptake were elevated because of the presence of autoantibodies. Thyroid hormone autoantibodies must be considered when clinicians encounter patients with unexplained abnormal results of thyroid function tests.
authors.affiliation: Section of Endocrinology, Diabetes, and Nutrition, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: Sara M
authors.initials: SM
authors.lastname: Pietras
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Safer
mesh_terms: D001323:Autoantibodies / Q000276:immunology*; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D013960:Thyroid Function Tests / Q000379:methods*; D013963:Thyroid Hormones / Q000276:immunology*; D013974:Thyroxine / Q000008:administration & dosage / Q000276:immunology / Q000627:therapeutic use
chemical_list: D001323:Autoantibodies; D013963:Thyroid Hormones; D013974:Thyroxine