[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Endocrine](https://durgical.com/en/physiology/#s-endocrine) › Measuring hormones: stimulation and suppression tests [Physiology](https://durgical.com/en/physiology/) · [Endocrine](https://durgical.com/en/physiology/#s-endocrine) # Measuring hormones: stimulation and suppression tests - Measurement - Exam priority: medium If a hormone is thought to be missing, the gland is stimulated; if it is thought to be in excess, the test tries to suppress it. Updated 2026-11-01 Also called: Dynamic tests, Immunoassays **See it in 3D:** [Right adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland-abdomen/) · [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/) ## Key points - Rule: suspected deficit → stimulation test; suspected excess → suppression test. - Adrenal insufficiency: stimulation with synthetic ACTH (cosyntropin); cortisol does not rise enough. - Hypercortisolism: low-dose overnight dexamethasone; a healthy person suppresses morning cortisol, Cushing syndrome does not. - Acromegaly: an oral glucose load fails to suppress GH; IGF-1 integrates GH secretion and is the first test. - Always read the pair: cortisol with ACTH, free T4 with TSH, calcium with PTH, glucose with insulin. ## What it is A single hormone level often misleads because many hormones are pulsatile, circadian or change with stress. So the pair (trophic hormone and final hormone) is always measured and, when needed, the axis is challenged. Dynamic tests use feedback: a healthy gland responds to stimulation and switches off with suppression; a diseased gland does not. ## Key facts - Immunoassays (ELISA, chemiluminescence) use antibodies; they can fail through interference (biotin, heterophile antibodies). - Hook effect: with extremely high prolactin (macroprolactinoma) a two-site assay can read falsely low; the sample is re-run diluted. - Estrogen raises CBG and TBG: high total cortisol and total T4 without excess free hormone. - Timing matters: cortisol and ACTH at 8 a.m.; testosterone in the morning; a single GH value means little because of its pulsatile secretion. ### Hormone axes and feedback **Lesion** Addison disease **Pattern** CRH ↑ · ADH ↑ · ACTH ↑ · Cortisol ↓ #### Primary hypofunction: Addison disease **Pattern:** CRH ↑ · ADH ↑ · ACTH ↑ · Cortisol ↓ The target gland fails: its hormone falls and, without negative feedback, the pituitary and hypothalamic hormones rise. Cortisol ↓ with ACTH ↑ → hyperpigmentation (MSH). Aldosterone also falls: hyperkalemia, hyponatremia, hypotension and salt craving. Exam rule: if the pituitary hormone moves opposite to the gland hormone, the problem is in the gland (primary); if they move together, it is central (pituitary or hypothalamus). - Stimulates (+) - Inhibits / negative feedback (−) - Level ↑ - Level ↓ Illustrative schematic drawn by Durgical: simplified axes and classic lab patterns; not for clinical decisions. ## Classic dynamic tests | Test | What for | Normal response | Abnormal result | | --- | --- | --- | --- | | [Synthetic ACTH stimulation](https://durgical.com/en/conditions/adrenal-insufficiency/) | Adrenal insufficiency | Cortisol clearly rises | Flat response | | [Low-dose dexamethasone suppression](https://durgical.com/en/conditions/cushing-syndrome/) | Screening for Cushing syndrome | Morning cortisol suppressed | Fails to suppress | | [High-dose dexamethasone suppression](https://durgical.com/en/conditions/cushing-syndrome/) | Source of ACTH-dependent Cushing | — | Suppresses: pituitary; does not: ectopic | | [Oral glucose load with GH](https://durgical.com/en/conditions/pituitary-adenoma/) | Acromegaly | GH falls | GH does not fall or rises | | Water deprivation | Polyuria with dilute urine | Urine concentrates | Urine stays dilute (diabetes insipidus) | | Insulin-induced hypoglycemia | GH and ACTH reserve | GH and cortisol rise | Low response (hypopituitarism) | ## Clinical notes - Before a suppression test, drugs that change dexamethasone metabolism or CBG (oral contraceptives, enzyme inducers) are reviewed. - In recent secondary adrenal insufficiency the ACTH test can be normal because the gland has not yet atrophied. ## Memory aid "Push what is missing, brake what is extra": a healthy gland obeys both orders. ## Test yourself Think of the answer, then tap the question to see it. ## Why does dexamethasone suppress cortisol in a healthy person but not in Cushing syndrome from an adrenal tumor? Dexamethasone brakes CRH and ACTH by feedback. The adrenal tumor makes cortisol on its own, without needing ACTH, so it does not switch off. ## Why does high-dose dexamethasone usually suppress pituitary Cushing disease but not ectopic ACTH? The corticotroph adenoma keeps some feedback sensitivity, only with a higher set point; an ectopic ACTH-secreting tumor lacks that regulation. ## Why is IGF-1 measured instead of a single GH level when looking for acromegaly? GH is secreted in pulses and swings widely through the day; IGF-1 has a long half-life and reflects integrated GH secretion. ## What is the hook effect and when does it matter? At an extreme concentration the antigen saturates both assay antibodies and the result reads falsely low; it matters in macroprolactinomas and is avoided by diluting the sample. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/measuring-hormones-stimulation-and-suppression-tests/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Right adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland-abdomen/) - [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/) ## Related topics - [Hormones: types, receptors and feedback](https://durgical.com/en/physiology/hormones-types-receptors-and-feedback/) - [The HPA axis and its circadian rhythm](https://durgical.com/en/physiology/the-hpa-axis-and-its-circadian-rhythm/) - [The thyroid axis: reading TSH and free T4](https://durgical.com/en/physiology/the-thyroid-axis-reading-tsh-and-free-t4/) - [Growth hormone and IGF-1](https://durgical.com/en/physiology/growth-hormone-and-igf-1/) - [Blood glucose, glucose tolerance test and HbA1c](https://durgical.com/en/physiology/blood-glucose-glucose-tolerance-test-and-hba1c/) - [The posterior pituitary: ADH and oxytocin](https://durgical.com/en/physiology/the-posterior-pituitary-adh-and-oxytocin/) ## Related conditions - [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/) - [Adrenal insufficiency](https://durgical.com/en/conditions/adrenal-insufficiency/) - [Pituitary adenoma](https://durgical.com/en/conditions/pituitary-adenoma/) ## In Biochemistry - [ELISA (enzyme-linked immunosorbent assay)](https://durgical.com/en/biochemistry/topics/elisa/) - [Cortisol](https://durgical.com/en/biochemistry/molecules/cortisol/) [← All of physiology](https://durgical.com/en/physiology/) Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given. Sources: [Cortisol Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/cortisol-test/) (MedlinePlus, US National Library of Medicine, 2024); [Hypercortisolism (Cushing Syndrome)](https://www.ncbi.nlm.nih.gov/books/NBK551526/) (StatPearls (NCBI Bookshelf), 2024); [Adrenal Insufficiency](https://www.ncbi.nlm.nih.gov/books/NBK441832/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 75). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/measuring-hormones-stimulation-and-suppression-tests/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/measuring-hormones-stimulation-and-suppression-tests/