Introduction and aim: Considering thehigh relative frequency of hypothyroidism in the community and the importance of proper diagnosis and treatment of this disease in the regions, the present study aimed to investigate the frequency distribution of positive thyroid peroxidase antibody (TPOAb) in patients with clinical and subclinical hypothyroidism and related factors.

Materials and methods: In this cross-sectional study, 283 patients with hypothyroidism, who referred to the endocrinology clinic of Kowsar Hospital in Semnan during 6 months of 2019, were selected by simple random sampling method and after extracting the patients' information, the data were compared between the two groups of clinical and subclinical hypothyroidism. Data analysis was performed using statistical software.

Results: 94.3% of patients were diagnosed with clinical hypothyroidism and 5.7% were diagnosed with subclinical hypothyroidism. 51.9% had positive thyroid peroxidase antibody (TPOAb) TSH levels in patients with positive thyroid peroxidase antibody were significantly higher than patients with negative TPOAb (P = 0.003). The relative frequency of positive thyroid peroxidase antibodies in the group with clinical hypothyroidism was significantly higher than in patients with subclinical hypothyroidism (P = 0.018).

Conclusion: More than half of patients with hypothyroidism had positive thyroid peroxidase antibodies.high serum TSH level, and anti-thyroid peroxidase antibody titer are effective factors in the diagnosis of hypothyroidism and especially its clinical type.

Keywords: Anti-thyroid peroxidase antibody, Clinical hypothyroidism, Subclinical hypothyroidism