Study design and study population
This is a retrospective cohort study conducted between January 2016 and December 2018 in the Second Affiliated Hospital of Xinxiang Medical University (also known as Henan province Mental Health Center). Approval by the Ethics Committee of the Second Affiliated Hospital of Xinxiang Medical University was obtained prior to the commencement of the study.
Patients affected by major depression disorder and admitted to the participating hospital for antidepressant treatment during the study period with thyroid function tests made at admission and during hospitalization were included into this study. The diagnosis of major depressive disorder was made by two staff psychiatrists and confirmed by a third senior psychiatrist, following the “National Guidelines of Diagnosis and Treatment for Mental Disorders” in China and was coded by International Classification of Diseases, 10threvision (ICD-10).
Patients with a thyroid function test outside of the normal range (i.e., TSH: 0.27-4.20mU/L and free T4: 12.00-22.00pmol/L) or on l-thyroxine treatment at admission were excluded. Patients who met the following criteria were further excluded: 1) ongoing pregnancy or lactation, 2) alterations of hepatic or renal function, or other serious medical condition, 3) history of alcohol or other substance dependence, 4) primary thyroid diseases, or known medical conditions that affect thyroid function, or 5) used mood stabilizers (i.e. lithium, valproic acid, and oxcarbazepine et al.) or quetiapine during hospitalization.