Impaired secretion of TSH in critically ill patients with 'low T4-syndrome'

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Abstract
Thyroid and pituitary function was studied in 10 male and 6 patients female during critical non-endocrine disease. Low concentrations of TT3 [total triiodothyronine] were observed in each case. Seven patients out of whom 3 survived, presented with low levels of TT4 [total thyroxine] due to deficiency in TBG [thyroid binding globulin] in the presence of normal values of FTI [free thyroxine index] and FT [free thyroxine], while a low T4-syndrome, characterized by low concentrations of both TT4 and FT4 was seen in 9 patients, 8 of whom died 1 to 16 days after evaluation of pituitary function. A diminished response of TSH to i.v. TRH (400 .mu.g), as observed in 4 patients with normal FT4 and in all patients with low T4-syndrome, was not accompanied by a concomitant lack in stimulated release of LH [luteinizing hormone], FSH and Prl [prolactin] in the majority of cases. However, the secretory maximum of LH and FSH following stimulation by LHRH (100 .mu.g i.v.) was delayed in 10 and in 9 patients, respectively, including patients both with normal and subnormal concentrations of FT4. From the above it appears that low stimulated concentrations of TSH in the presence of subnormal concentrations of FT4 indicate an extremely poor prognosis in critically ill patients. The abnormal behavior of TSH in this group of patients cannot be explained by generalized pituitary insufficiency or by an increase in FT4.