Do We Still Need the TRH Stimulation Test?

Abstract

Objective: To evaluate the diagnostic value of the thyrotropin-releasing hormone (TRH) stimulation test in the diagnosis of central hypothyroidism in patients with Sheehan's syndrome. Design: TRH stimulation test was performed in 72 patients with Sheehan's syndrome. Basal free triiodothyronine (fT₃) and free thyroxine (fT₄) levels were measured. Serum thyrotropin (TSH) concentration was determined before and 30, 60, 90, and 120 minutes after 200 μg TRH IV bolus injection. The peak TSH values <5.5 μIU/ml were defined as inadequate response. A peak TSH at 60 minutes or later was considered as delayed response. If TSH (60 minutes after peak), was more than 40% of the peak value it was considered as prolonged response. The diagnosis of central hypothyroidism (CH) was made if either serum fT₄ concentration was subnormal with an inappropriately low serum TSH concentration or inadequate response to TRH stimulation test and/or a delayed or prolonged response to TRH stimulation test. Main outcome: Fifty-six (77.7%) of the patients had low serum fT₄ and fT₃ levels with an inappropriately low serum TSH levels were defined as CH (CH0 group). Ten (13.8%) patients with normal and low-normal fT₄ levels had no response and/or delayed or prolonged response to TRH stimulation test (CH1group). Six (8.3%) patients had fT₃, fT₄, and TSH levels within normal limits and peak TSH responses ≥5.5 μIU/ml consistent with euthyroidism (euthyroid group). Thus, 66 (91.6%) of 72 patients with Sheehan's syndrome had CH. Although fT₄ levels were within normal reference range, TRH stimulation test revealed that 10 (13.8%) of these had CH. Conclusion: TRH stimulation test is useful in the diagnosis of central hypothyroidism, especially in whom fT₄ and/or TSH is low-normal and known to have hypothalamo-pituitary pathology.