Diagnostic value of the TRH test for central hypothyroidism in patients with pituitary and parasellar tumors: a single-center retrospective cross-sectional study.

PURPOSE: The utility and diagnostic interpretation of the thyrotropin-releasing hormone (TRH) test for diagnose central hypothyroidism (CeH) remain unclear. METHOD: To understand the significance of TRH testing for the diagnosis of CeH we reviewed the medical charts of 105 patients who underwent TRH test (200 µg) and analyzed TSH values and responses in three groups. Group 1, the control group, included 25 participants without pituitary and parasellar tumors (PPTs), and with normal pituitary function. Group 2, the CeH group, included 13 patients with PPTs and low free thyroxine (fT4) levels. Group 3 included 67 patients with PPTs but normal fT4 levels. RESULTS: Basal TSH levels did not significantly differ between Group 1 and Group 2. After TRH test, a peak TSH value and fold-TSH response were significantly lower in Group 2. Group 2 showed a higher rate of delayed and prolonged TSH responses and lower fold-free triiodothyronine (fT3) responses. We determined the cut-off values of fold-TSH, prolonged response, and fold-fT3 responses for diagnosing CeH patients with high sensitivity and specificity. Using two or more of these cut-off values further reduced the false-positive rate to 4%. Group 3 had a higher rate of positive results than Group 1, suggesting that there are patients with hidden CeH. CONCLUSION: In this study, we revealed that CeH can be diagnosed with a TRH test with a probability of more than 90%, and the test may be useful for diagnosing the CeH in patients with normal fT4 levels.