What is secondary hypothyroidism?

Underactive thyroid: Hormone in blood stream due to pituitary insufficiency thyroid gland fine, but pituitary gland not working corectly.

Unstimulated thyroid: Hypothyroidism describes a situation in which the thyroid gland doesn't produce normal amounts of thyroid hormone (t4). In primary hypothyroidism, the thyroid can't make enough thyroid hormone. T4 levels are low, and TSH (thyroid stimulating hormone) is high. In secondary hypothyroidism, the thyroid can work normally, but due to low levels of tsh, doesn't (t4 & TSH levels both low or low-normal).

Not primarily thyroi: Hypothyroidism can be primary - caused by a weak thyroid gland or secondary to other hormonal problems, like a pituitary problem. Or your thyroid can become dysfunctional secondary to high insulin, estrogen or cortisol. If you have functional hypothyroidism, this problem can go undetected by routine screening tests. More extensive testing can often reveal abonormalities. This is very common.