title: Euthyroid hyperthyroxinemia and thyroxine-binding prealbumin excess in islet cell carcinoma.
abstract: This manuscript describes euthyroid hyperthyroxinemia secondary to elevated serum T4-binding prealbumin (TBPA) concentrations in a patient with islet cell carcinoma and reports serum TBPA measurements in other patients with islet cell carcinoma. A 73-yr-old man with a 17-yr history of metastatic islet cell carcinoma was found to have hyperthyroxinemia. His total serum T4 concentration was 18.5 micrograms/dl (normal, 5.5-11.5). Eight years previously, his serum T4 concentration was normal. His free T4 concentration, as determined by equilibrium dialysis, was 1.3 ng/dl (normal, 0.9-2.1). Serum T3, TSH, and T4-binding globulin (TBG) concentrations were normal, as was the TSH response to TRH administration. Polyacrylamide gel electrophoresis of the patient's serum in the presence of tracer amounts of [125I]T4 revealed that, compared to normal sera, [125I]T4 binding to TBPA was increased from 30.0 +/- 6.0% (mean +/- SD) to 52.0%. The distribution of [125I]T3 amont albumin, TBG, and TBPA was normal in this electrophoretic procedure. The concentration of TBPA in the patient's serum was 189 mg/dl. In contrast, the mean serum TBPA concentration in normal men was 40 +/- 4 (mean +/- SD) mg/dl, and that in normal women was 18 +/- 4 mg/dl. Sera from the patient's daughter, his brother, 2 sisters, and 2 male paternal cousins contained normal amounts of TBPA, ranging from 34-47 mg/dl in his male relatives and from 26-30 mg/dl in his female relatives. Serum free T4 index determinations in his relatives also were normal. Serum TBPA concentrations were determined in 14 additional patients with islet cell carcinoma. In 1 of these patients, a man with an insulinoma, serum TBPA was elevated (66 mg/dl). This patient's serum T4 level was 7.3 micrograms/dl, and his free T4 index was 7.0. These data and another study suggest that islet cell carcinoma may rarely produce a TBPA-like protein resulting in an elevated serum TBPA concentration. Markedly elevated serum TBPA is associated with euthyroid hyperthyroxinemia.
authors.forename: R
authors.initials: R
authors.lastname: Rajatanavin
authors.forename: C
authors.initials: C
authors.lastname: Liberman
authors.forename: G D
authors.initials: GD
authors.lastname: Lawrence
authors.forename: C M
authors.initials: CM
authors.lastname: D'Arcangues
authors.forename: R A
authors.initials: RA
authors.lastname: Young
authors.forename: C H
authors.initials: CH
authors.lastname: Emerson
mesh_terms: D007516:Adenoma, Islet Cell / Q000097:blood* / Q000235:genetics; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D010190:Pancreatic Neoplasms / Q000097:blood* / Q000235:genetics; D011228:Prealbumin / Q000378:metabolism*; D011485:Protein Binding; D012016:Reference Values; D012709:Serum Albumin / Q000378:metabolism; D013974:Thyroxine / Q000097:blood*; D013975:Thyroxine-Binding Proteins / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood
chemical_list: D011228:Prealbumin; D012709:Serum Albumin; D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine; D013974:Thyroxine