Serum thyrotropin in hospitalized psychiatric patients: Evidence for hyperthyrotropinemia as measured by an ultrasensitive thyrotropin assay

Abstract

In order to gather further insight into the basis for high serum T4 and/or T3 of psychiatric illnesses, we studied thyroid function in 84 consecutive newly hospitalized psychiatric patients (HPP) in a 12-week period. Serum T4 and T3 were measured by immunoassay and thyrotropin (thyroid-stimulating hormone [TSH]) by an ultrasensitive immunoradiometric assay. Serum T4 was in the normal range in 64 (76%) and elevated in 20 (24%); free T4 index was elevated in 13 of 75 (16%), total T3 in 12 of 60 (20%), free T3 index in seven of 56 (13%), and TSH in 14 of 84 (17%) cases so studied. Serum TSH was subnormal in only one case (1%). Among the 14 patients with elevated serum TSH, serum free T4 index was normal in 12 and elevated in two. High serum T4 (or free T4 index) and high serum TSH were not correlated significantly by χ 2 analysis. None of the patients with elevated TSH demonstrated goiter or antithyroglobulin or antimicrosomal antibodies. On repeat testing 7 to 21 days after admission, serum TSH (and/or T4) normalized in the three of five patients studied. Serum TSH response to 500 μg intravenous (IV) thyrotropin-releasing hormone (TRH) was normal (serum TSH post-TRH, 8 to 28 μU/mL) in two patients with elevated TSH and T4, one patient with normal TSH and high T4, and one patient with normal TSH and T4. One patient with suppressed serum TSH (0.1 μU/mL) had elevated serum T4 (16.9 μg/dL, normal 4.8 to 11.5). In conclusion, in HPP (1) elevated serum T4 (or free T4 index) is mainly associated with normal or elevated serum TSH; TSH is suppressed in only 1%; (2) the transiency of high TSH (and T4) and absence of goiter and antithyroid antibodies suggest that high TSH (and T4) values are a result of a central abnormality in the central nervous system (CNS)-hypothalamothyrotropic axic.