Drug-induced hypothyroidism (i.e. amiodarone or lithium)
Hypothyroidism after radiation treatment
Central hypothrydoisim (rare - i.e. pituitary apoplexy, surgery, radiation, drug-induced)
What is the most common cause of hypothyroidism in Canada?
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.
What is Hashimoto’s Disease?
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.
What are anti-TPO Antibodies?
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.
When is ordering an anti-TPO antibody useful?
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.
I have a positive anti-TPO Antibody. Do I need to re-measure anti-TPO antibodies?
Auto-immune thyroiditis (Hashimoto’s disease) is a chronic condition and repeat measurement is not necessary.