|A blood test is needed to confirm the diagnosis of an underactive thyroid gland, but does not necessarily tell you the cause. The patientís clinical history and results of antibody screening tests and thyroid scans can help to determine the underlying cause.
Blood tests will measure the levels of TSH, the thyroid stimulating hormone, and T3 and T4, the thyroid hormones - as well as their interactions with each other.
The results of these tests will tell you where the problem lies - in the pituitary gland, where TSH is produced, the hypothalamus (which controls the pituitary gland) or in the thyroid gland itself. This will in turn help physicians to determine the correct management for you.