SAT-108 Thyrotropin Level Predicts Postoperative Hypothyroidism in Patients with Nonfunctioning Pituitary Masses

Abstract Disclosure: Y. Seki: None. N. Takano: None. S. Takebe: None. S. Kitayama: None. K. Hirata: None. D. Watanabe: None. Y. Oda: None. K. Amano: None. T. Kawamata: None. A. Ichihara: None. Context: Central hypothyroidism (CH) is a common complication of nonfunctioning pituitary masses. However, no predictive marker for future CH risk in patients with nonfunctioning pituitary masses has been established.Objective: To identify predictive markers for postoperative CH in patients with nonfunctioning pituitary masses. Methods: We retrospectively analyzed basal thyrotropin (TSH), peak TSH response to thyrotropin-releasing hormone (TRH), peak/basal TSH ratio, delayed TSH response, and free thyroxine (FT4) levels before and 1 year after pituitary surgery in patients with nonfunctioning pituitary neuroendocrine tumors or Rathke’s cleft cysts. Results: Among 155 patients, pituitary mass sizes were significantly inversely correlated with FT4 levels (rs = -0.30, P < 0.001). FT4 levels were significantly inversely correlated with both basal TSH levels (rs = -0.23, P = 0.004) and peak TSH response to TRH (rs = -0.19, P = 0.020). One-year post-surgery, 22 (28%) of 78 reassessed patients exhibited hypothyroidism. Logistic regression revealed that higher preoperative basal TSH levels (≥ 1.78 mIU/L) were significantly associated with increased risks of postoperative hypothyroidism, while a higher peak/basal TSH ratio (≥ 9.24) was associated with a lower risk, independent of preoperative hypothyroidism. The area under the curve for peak/basal TSH ratio in predicting postoperative hypothyroidism was not significantly different from that for basal TSH (P = 0.73). Conclusion: Preoperative TSH levels in the upper reference range may reflect impaired TSH secretion capacity, predicting postoperative CH in patients with nonfunctioning pituitary masses. Presentation: Saturday, July 12, 2025