Source / episode info
- **Episode:**602
- **Title:**DIP Ep 602: Endocrine Thinking (Stimulation and Suppression Tests)
- **Published:**2025-05-14
- Source:Episode page
One-liner
This episode provides an advanced review of endocrine physiology, detailing the principles and specific interpretations of suppression and stimulation tests for major axes including HPA (Cushing's), RAAS (Conn's), ACTH (Addison's), GH, and Gonadotropins.
High-yield summary
- General Principle: Suppression tests are used when a condition involves excess hormone; stimulation tests are used when hormones are low. Both serve as confirmatory diagnostics after initial screening.
- Cushing Syndrome Differentiation (HDDST): High Dose Dexamethasone suppresses cortisol in Cushing's Disease (pituitary adenoma) but fails to suppress it if the cause is an adrenal adenoma or ectopic ACTH source.
- Primary Hyperaldosteronism (Conn's): Diagnosis relies on a high Aldosterone/Renin Ratio (>20–30). Confirmation requires failure of aldosterone suppression following salt load, saline infusion, or ACE inhibitor administration (Captopril).
- Addison's Disease: Confirmed by the Cosyntropin stimulation test; cortisol fails to rise despite exogenous ACTH administration.
- Acromegaly/Gigantism: Confirmatory diagnosis uses the Glucose Suppression Test: GH fails to suppress following an oral glucose load.
- Gonadotropin Axes: GNRH stimulates LH and FSH in central precocious puberty, but failure of response suggests pituitary or hypothalamic dysfunction (hypogonadotropic hypogonadism).
Learning objectives
- Differentiate between Cushing's Disease (pituitary adenoma), adrenal adenoma, and ectopic sources using appropriate suppression tests.
- Interpret the results of primary hyperaldosteronism diagnostic tests (Aldosterone/Renin Ratio, salt loading).
- Apply stimulation testing principles to diagnose primary adrenal insufficiency (Addison's) versus secondary causes.
- Understand the physiological basis for failure of GH suppression in acromegaly and aldosterone suppression in Conn's syndrome.
- Interpret gonadotropin axis function using GNRH stimulation tests to differentiate central vs. peripheral endocrine failures.