The thyroid hormone panel (also known as the thyroid function panel), which examines the quantity of thyroid hormone in the blood, is widely used to detect hypothyroidism. However, in some cases, it is not that straightforward, and more thorough testing is required. This is why, in order to properly diagnose and treat hypothyroidism, a good relationship with a qualified endocrinologist is nearly always required.
All thyroid hormones have typical ranges that have been established using computers that measured these hormones in tens of thousands of people. Hypothyroidism is diagnosed when your thyroid hormone levels fall below the normal range. The T4 (thyroxine) and TSH (thyroid stimulating hormone) levels are measured in the thyroid function test (TSH).
T4 (the major thyroid hormone) levels in the blood will be low, while TSH levels will be high, in the most frequent form of hypothyroidism, in which the thyroid gland itself is underperforming. This indicates that the thyroid is not producing enough hormone, and the pituitary gland recognizes this and responds correctly by producing more TSH in an attempt to coerce the thyroid into producing more hormone.
The thyroid hormone T4 will be low in hypothyroidism caused by pituitary failure, but the TSH level will also be low. Because it can only make hormones in response to TSH signals from the pituitary gland, the thyroid is responding “appropriately” in these circumstances.