Medicinenet has a good explanation of the thyroid peroxidase test.
Thyroid peroxidase (TPO) is an enzyme made in the thyroid gland that is important in the production of thyroid hormone...
Thyroid peroxidase test is a test that measures the level of an antibody that is directed against thyroid peroxidase (TPO).
Autoantibodies to thyroid peroxidase (TPOAb) are produced within the body. The presence of TPOAb in the blood reflects a prior attack on the thyroid tissue by the body's immune system.
The GH peak response to pharmacological stimulation and the plasma IGF I concentration in young adults with GHD of childhood onset depend on the presence of additional pituitary deficiencies, reflecting a more severe defect of the hypothalamic-pituitary axis. The sex steroids cannot increase the IGF I if the GH secretion is zero.