Endocrine diagnostics and pharmacotherapy require understanding of hormonal axes, feedback loops, and the pharmacological manipulation of receptor signaling. Thyroid function assessment relies on TSH as the most sensitive screening test, with free T4 confirming the diagnosis — elevated TSH with low free T4 indicates primary hypothyroidism, while suppressed TSH with elevated free T4 indicates hyperthyroidism. Diabetes management centers on achieving glycemic targets through insulin therapy (type 1) or a stepwise pharmacological approach beginning with metformin (type 2), with HbA1c reflecting average glycemic control over the preceding 2-3 months. Adrenal insufficiency diagnosis requires early morning cortisol levels and ACTH stimulation testing, with cortisol replacement therapy requiring stress dosing during illness or surgery.