Synopsis
Choose stimulation or suppression testing for a defined endocrine question, prepare the patient and assay correctly, supervise predictable hazards, and interpret the complete response rather than one number.
- A stimulation test asks whether an axis with possible deficiency can respond; a suppression test asks whether suspected autonomous secretion can be switched off.
- Write the clinical question before booking: the same test can be inappropriate when pre-test probability, recent treatment or acute illness changes.
- Use the endocrine unit's current protocol because dose, sampling times, assay-specific thresholds, contraindications and rescue arrangements differ between laboratories.
Key red flags
Compatible symptoms during a low laboratory plasma glucose that resolve with correction establish the clinical event and can justify a supervised fast or meal test selected by timing.
Investigation priorities
Assess adrenal cortisol secretory reserve when basal morning assessment remains indeterminate or specialist confirmation is needed.
Management branches
Basal tests and phenotype leave a clinically important endocrine diagnosis unresolved.
- Define whether the suspected abnormality is deficient reserve or autonomous excess, and quantify pre-test probability using phenotype, paired basal hormones and medicines.
- Choose the validated stimulation or suppression test whose result will change treatment, referral or imaging, confirming that a simpler repeat sample cannot answer it.
Key medicines
Tetracosactide (Synacthen)For the licensed adult 30-minute test, give tetracosactide 250 micrograms once by intramuscular or intravenous injection after the baseline cortisol sample, then collect cortisol exactly 30 minutes later.
Dexamethasone for suppression testingFor a standard adult overnight suppression test, give dexamethasone 1 mg orally at 23:00 and obtain serum cortisol at 09:00 the next morning, using the endocrine laboratory's validated interpretation.