​Thyroid Stimulating Hormone (TSH): Most common screening lab test for hyper or hypothyroidism.
Produced by: Pituitary gland (brain).
Purpose: The pituitary gland monitors blood thyroid hormone levels (T4, T3) and will produce a specific amount of TSH which travels to the thyroid gland to stimulate production of T4 and T3. The lower the TSH level is the less stimulation there is for the thyroid gland to produce thyroid hormone
Lab Reference Range: 0.4 – 4.5 mIU/L
When to order:
- To screen for hypothyroidism (low) or hyperthyroidism (high).
- To monitor thyroid hormone medication usage.
Pearls:
- High TSH means low thyroid function.
- Some physicians consider a TSH greater than 3.0 to be abnormally high and may treat with a test dose of thyroid hormone to see if signs and symptoms improve.
- If TSH is below the normal range and thyroid medication is not being used, you must rule out Grave’s Disease or hyperthyroidism.
- After thyroid cancer removal, a physician will keep the TSH below normal to prevent reoccurrence (TSH suppression). So, in this case, a TSH less than 0.4 would be considered optimal.
- If you are on thyroid hormone and your TSH is below normal, your medication may be making you hyperthyroid. Symptoms may include: anxiety for no reason, palpitations, heart fluttering, sweating all the time, or you feel like you just drank five coffees. See your doctor.