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RAJATA RAJATANAVIN, CLAUDIO LIBERMAN, GEORGE D. LAWRENCE, CATHERINE M. D'ARCANGUES, RUTH A. YOUNG, CHARLES H. EMERSON, Euthyroid Hyperthyroxinemia and Thyroxine-Binding Prealbumin Excess in Islet Cell Carcinoma, The Journal of Clinical Endocrinology & Metabolism, Volume 61, Issue 1, 1 July 1985, Pages 17–21, https://doi.org/10.1210/jcem-61-1-17
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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 Mg/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 Mg/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.
