This anti-thyroid peroxidase (TPO) is an auto antibody to an integral part of thyroid cell microsomal membrane, and is a confirmation test for a diagnosis of Hashimoto's thyroiditis. Also sometimes called thyroid antimicrosomal antibody. Present in significant titers in Hashimoto's thyroiditis and Grave's disease. Anti-thyroid peroxidase can also be present with any process causing active chronic destruction of follicles, even such as diffuse sclerosing variant of papillary thyroid cancer.

References:

1. thyroid tests Practice Guidelines, National Academy of Clinical Biochemistry (NACB), USA.