There are 2 thyroid hormones produced by thyroid gland. Thyroid gland is a small butterfly shaped gland , in front of your neck, below the Adam’s apple. Thyroid gland produces T3-triiodothyronine and T4-thyroxine by using iodine. TSH – thyroid stimulating hormone is secreted by pituitary gland and stimulates thyroid gland for thyroid hormone production.
Thyroid gland mostly produces T4 and a small amount of T3. T3 is the active type in the thyroid hormones, T3 does the main part of the work in your body. For this reason liver converts T4 to T3 for body usage.
TSH hormone is produced in brain by pituitary gland and regulates thyroid hormone level. If thyroid hormone level is high TSH production decreases, also TSH level increases if thyroid gland can’t produce enough thyroid hormones. TSH production is opposite to thyroid hormone production.
TSH- thyroid stimulating hormone normal levels
- Newborn ( under 4 days) : 1-39 mU/L ( miliunits per liter)
- Children: 7-6.4 mU/L
- Adult: 0.4-4.2 mU/L
High TSH- thyroid stimulating hormone causes
If TSH level is normal but thyroid gland can’t produce enough thyroid hormones this is called primary hypothyroidism, also known as underactive thyroid. Body commands thyroid gland for thyroid hormone production but thyroid gland can’t produce enough. Thyroid hormone level decreases and pituitary secretes more TSH to increase thyroid production. If thyroid gland can response properly, thyroid hormone level increases to normal level. If thyroid gland can’t response to this request, thyroid deficiency symptoms occur.
TSH level increases in hypothyroidism condition, this is the most common cause of high TSH level.
Low TSH- thyroid stimulating hormone causes
Hyperthyroidism is the excessive levels of thyroid hormone production in thyroid gland. Body reduces TSH production to regulate thyroid hormone level. Thyroid hormone production request decreases to thyroid gland and body tries to regulate the condition. This condition is called primary hyperthyroidism or overactive thyroid gland.
TSH level may decrease if pituitary gland damaged by any reason. This is secondary hyperthyroidism. Common cause is TSH secreting pituitary adenoma ( tumor).
TSH &T3&T4 level relation
TSH level should be evaluated with thyroid hormones level as you can see;
|TSH level||T3 and T4 level||Cause|
|Low||High||Graves disease, thyroid nodule|