International Journal of Preventive Medicine (Int J Prev Med)2008-78021392022102227102710ENDepartment of Endocrinology, Vali‑Asr Hospital, Endocrinology and Metabolism Research Center (EMRC), Imam Khomeini Complex Hospital & Endocrinology and Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, TehranDepartment of Endocrinology, Vali‑Asr Hospital, Endocrinology and Metabolism Research Center (EMRC), Imam Khomeini Complex Hospital, Tehran University of Medical Sciences, TehranBrighton and Sussex Medical School, Division of Medical Education, BrightonDepartment of Epidemiology, Non‑Communicable Diseases Research Center, Alborz University of Medical Sciences, KarajDepartment of Endocrinology, Vali‑Asr Hospital, Endocrinology and Metabolism Research Center (EMRC), Imam Khomeini Complex Hospital, Tehran University of Medical Sciences, TehranDepartment of Laboratory Sciences, School of Paramedical Sciences, Mashhad University of Medical Sciences, Mashhad20221018<strong>Background</strong>: Oxidative stress (OS) is caused by an imbalance between prooxidant substance production and antioxidant defense. OS is involved in physiologic interactions in the body and the pathogenesis of various disorders. This study aimed to evaluate serum prooxidant‑antioxidant balance (PAB) as a selective prooxidant, antioxidant defense, and acute phase reactant protein in patients with subclinical and clinical hypothyroidism. <strong>Methods</strong>: This case‑control study was conducted in three groups including clinical hypothyroidism (32 patients), subclinical hypothyroidism, (42 cases), and healthy controls (32 individuals). This study was performed in the Endocrine Clinic of Arash Training and Research Hospital, Tehran, 2017. In the study groups, thyroid hormones including T4 and Thyroid Stimulating Hormone (TSH), fasting blood glucose (FBG), lipid profile, PAB, and hs‑CRP as inflammatory markers were measured and compared between the groups. <strong>Results</strong>: Among 106 participants, 95.3% were females, the gender balance was similar across groups and mean age was 30.79 ± 7.65 years. FBG and lipid profile except for cholesterol level were not significantly different between the three study groups. However, cholesterol level in the clinical hypothyroid group was significantly higher than the other two groups. PAB was higher in subclinical hypothyroidism compared to healthy controls after adjustment for age and TSH levels (P value: 0.04) but there was no significant difference in the clinical hypothyroid group in comparison with healthy controls. In addition, there was no significant difference in high‑sensitivity C‑reactive protein (hs‑CRP) between the three study groups. <strong>Conclusions</strong>: This study suggests that that subclinical hypothyroidism increases PAB in comparison to healthy control which could indicate OS response in patients with subclinical hypothyroidism, respectivelyhttp://ijpm.mui.ac.ir/index.php/ijpm/article/view/2710http://ijpm.mui.ac.ir/index.php/ijpm/article/download/2710/717718551