Thyroid Peroxidase Examination: This blood test is used to identify autoantibodies targeting peroxidase (TPO), an essential enzyme for thyroid hormone production. TPO is located within thyroid follicle cells and plays a crucial role in the iodination of T4 and T3 during thyroid hormone synthesis. The body itself produces autoantibodies against thyroid peroxidase, known as TPOAb, which can attack and impair thyroid function. These antibodies are found in a significant percentage (70% to 90%) of individuals with chronic thyroiditis and are also present in smaller numbers in those with other thyroid conditions. Additionally, conditions like Sjogren's syndrome and other autoimmune disorders may sometimes test positive for TPOAb. A small percentage (approximately 3%) of people may have TPOAb without showing signs of disease. The likelihood of having TPOAb is higher in women and increases with age. This test is referred to by several names, including the thyroid peroxidase (TPO) antibody test, thyroid peroxidase autoantibody test, antimicrosomal antibody test, and antithyroid microsomal antibody test.