HPT Axis Dysregulation in Mood and Anxiety Disorders: The Clinical Utility of Routine Hormonal Dosing in Psychiatric In-Patients

Background/Objectives: Thyroid dysfunction is frequently associated with mood and anxiety disorders, yet the directionality and diagnostic specificity of this relationship remain debated. Although numerous studies have examined major depressive disorder (MDD) and bipolar disorder (BD) separately, comparative data including generalized anxiety disorder (GAD) and accounting for non-thyroidal illness (NTI) effects remain scarce. This study aimed to evaluate thyroid function and its correlation with affective symptom severity across MDD, GAD, and BD in an inpatient cohort. Methods: Eighty-eight hospitalized patients with MDD, GAD, or BD were included in the study (MDD = 30, GAD = 30, BD = 28). Serum levels of TSH, FT4, and FT3 were measured 24–48 h after admission to minimize the influence of NTI. Psychiatric assessment included the Montgomery-Åsberg Depression Rating Scale (MADRS), Hamilton Anxiety Scale (HAM-A), and Young Mania Rating Scale (YMRS). Between-group differences were analyzed using ANOVA, and associations between thyroid parameters and symptom severity were examined using correlation and regression analyses. Results: ANOVA revealed that patients with MDD had significantly higher TSH levels compared with those with GAD and BD (p < 0.01). MDD patients also showed a higher prevalence of subclinical hypothyroidism (33.3%) than patients with GAD (13.3%) and BD (7.1%), as well as a higher prevalence of overt hypothyroidism (13.3%) compared with GAD (0%) and BD (7.1%). TSH levels correlated positively with MADRS scores (r = 0.45, p < 0.05) and HAM-A scores (r = 0.38, p < 0.05), particularly within the MDD group. In BD, FT4 and FT3 levels were elevated and positively correlated with YMRS scores (FT4: r = 0.30, p < 0.05; FT3: r = 0.42, p < 0.05). In regression analysis within the MDD subgroup, both hypothyroidism and male sex were independently associated with higher MADRS scores, indicating greater depressive symptom severity. Conclusions: These findings suggest diagnosis-specific patterns of thyroid dysfunction among psychiatric inpatients. Higher TSH levels and increased rates of hypothyroidism were most prominent in MDD and were associated with greater depressive and anxiety symptom severity, whereas elevated FT4 and FT3 levels in BD were associated with manic symptom severity. The results support systematic thyroid screening in depressive admissions, hormone-informed monitoring in bipolar disorder, and a more integrated endocrine–psychiatric approach to clinical care.