Anti-Microsomal antibodies can be a sign of thyroid gland damage caused by the immune system. They may be measured if thyroiditis is suspected. Measuring thyroglobulin antibody levels after treatment for thyroid cancer can help your provider decide what the best test is to monitor you for a recurrence of the cancer. Thyroid peroxidase is a type of protein (called an enzyme) that cells in the thyroid gland use to make thyroid hormone. If these enzymes leak out into the bloodstream (as when thyroid cells are damaged) the immune system makes antibodies against these proteins.