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- Auto-immune hypothyroidism (AKA Hashimoto’s Disease)
- Hypothyroidism due to iodine deficiency
- Drug-induced hypothyroidism (i.e. amiodarone or lithium)
- Hypothyroidism after radiation treatment
- Central hypothrydoisim (rare - i.e. pituitary apoplexy, surgery, radiation, drug-induced)
Auto-immune hypothyroidism (AKA Hashimoto’s Disease) is the most common form of hypothyroidism in Canada. Iodine is a necessary nutrient to make thyroid hormone. In Canada, people generally have an adequate dietary intake of iodine through fortified foods (i.e. iodine-fortified table salt). Outside of developed countries like Canada, iodine deficiency is the most common cause of hypothyroidism.
Hashimoto’s Disease or Auto-immune hypothyroidism (the most common cause of hypothyroidism in Canada) occurs because your body’s immune system begins attacking its own thyroid gland. The immune system starts making antibodies to a component of your thyroid gland called Thyroid-Peroxidase and Thyroglobulin, causing it to become non-functional. These are called Anti-TPO Antibodies and Anti-Thyroglobulin Antibodies. Approximately 10% of people with Hashimoto’s Thyroiditis can be antibody negative however.
Anti-TPO antibodies when measured high, in the presence of an elevated TSH and low T4 suggest Auto-immune Hypothyroidism. Most guidelines do not recomment routine testing with anti-TPO antibodies as they are not necessary to make a diagnosis of hypothyroidism.
If you have a TSH between 4 and 10, with a normal Free T4, having anti-TPO antibodies can guide a physician to start treatment. A negative anti-TPO antibody might mean a doctor will monitor your TSH without starting medications if your TSH is between 4-10.
Auto-immune thyroiditis (Hashimoto’s disease) is a chronic condition and repeat measurement is not necessary.