When investigating many endocrinological diseases, basal laboratory parameters are not sufficient to distinguish between physiological and pathological hormone secretion. Functional diagnostics plays a decisive role in this context. Stimulation and suppression tests are used depending on whether under- or over-function needs to be diagnosed. This review article discusses selected functional tests, each of which plays an important role in current guidelines. Indications and test principles, including their performance, reliability, and limitations, are discussed. Topics covered include the ACTH stimulation test for the diagnosis of adrenal cortex insufficiency and the dexamethasone inhibition test for suspected Cushing's syndrome, as well as functional tests for the diagnosis of primary hyperaldosteronism, pheochromocytoma, acromegaly, growth hormone deficiency, thyroid nodules and suspicion of medullary thyroid carcinoma, insulinoma, and Zollinger-Ellison syndrome. Functional tests that are explicitly not recommended are also addressed.
