TPO and hypothyroidism: The rate of progression to overt hypothyroidism is assessed to be about 5% per year, based on a combination of an elevated level of TSH with the presence of thyroid autoantibodies, thyroid peroxidase (TPO) and anti-thyroglobulin (Tg), together with clinical signs and symptoms, such as fatigue, weight gain, increased sensitivity to cold, drowsiness and others [22, 31].