Overview
Start with the Axis, Not a Single Result
The pituitary is the control center for several endocrine axes, but a pituitary hormone value is rarely meaningful by itself.
The pituitary is the control center for several endocrine axes, but a pituitary hormone value is rarely meaningful by itself. Interpret the trophic hormone beside the hormone made by the target gland: - TSH with free T4 - ACTH with cortisol - LH and FSH with estradiol or testosterone - GH with IGF-1 A normal-looking pituitary value can be inappropriate when the target-gland hormone is low. In central hypothyroidism, for example, a low free T4 with a low, normal, or only mildly elevated TSH indicates inadequate pituitary or hypothalamic stimulation. The TSH is not “normal” in a physiologic sense; it has failed to rise enough for the degree of hypothyroxinemia. This differs from primary gland failure. Primary hypothyroidism usually produces low free T4 with clearly elevated TSH because the pituitary is responding appropriately. Primary adrenal insufficiency generally produces low cortisol with elevated ACTH. Central adrenal insufficiency produces low cortisol with ACTH that is low or inappropriately normal. A pituitary panel can reveal partial failure. One axis may be intact while another has failed, particularly early in pituitary disease. Progressive loss...