Background and PurposeSSNHL is a common otology emergency, that may lead to hearing loss and impact quality of life. This study aims to investigate the association of thyroid-related hormone levels with moderately severe-to-profound sudden sensorineural hearing loss (SSNHL) that may contribute to treatment optimization.MethodsThe study included 70 patients with moderately severe-to-profound SSNHL and 100 age- and sex-matched healthy controls. Peripheral venous blood samples were taken from the participants, and their thyroid-related hormone levels were measured at admission and one week after treatment.ResultsThyroid-related hormone levels of total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH) (all P < 0.05) were found to be at significantly lower levels in moderately severe-to-profound SSNHL patients to that of the control group. The increases of TT3, TT4, FT3, and TSH levels were significantly higher in the effective group than that in the ineffective group (all P < 0.05). Through receiver operating characteristic curve analyses, areas under the curve were 0.737, 0.636, 0.837, 0.458, and 0.903 for TT3, TT4, FT3, FT4, and TSH, respectively. Linear correlation analysis revealed that TSH level (R = 0.707, P < 0.05) elevation after treatment successfully predicted a favorable outcome of hearing recovery. Logistic regression analyses suggest low FT3 and TSH levels to be independent occurrence predictors while the increase of TSH level may be an independent favorable outcome predictor.ConclusionsThe results suggest low FT3 and TSH levels are risk factors for moderately severe-to-profound SSNHL. By discovering the positive association between TSH elevation and hearing recovery, along with the potential novel predictors of FT3 and TSH, our study may contribute valuable insights to the study and treatment of moderately severe-to-profound SSNHL.Trial RegistrationChinese Clinical Trial Registry; ChiCTR1800017072. Registered 10 July 2017, http://www.chictr.org.cn/showproj.aspx?proj=29023