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Adrenal insufficiency and adrenal crisis
In primary insufficiency (Addison disease) both cortisol and aldosterone are lacking and ACTH is high (hyperpigmentation, hyperkalaemia); in secondary insufficiency only cortisol is lacking and ACTH is low; and in an adrenal crisis hydrocortisone is given at once, without waiting for results.
Why it matters in the exam
Questions present weakness, weight loss, abdominal pain, low blood pressure and salt craving, sometimes with hyponatraemia and hyperkalaemia on the laboratory sheet — and ask the candidate to identify Addison disease and choose a test. Remember that a very low morning cortisol is suspicious, but the diagnosis is made with an ACTH stimulation test (cosyntropin 250 µg): a peak cortisol below 18 µg/dL at 30 or 60 minutes confirms insufficiency. A high ACTH points to a problem in the gland itself (primary), and a low ACTH to a pituitary problem or to withdrawal of steroid treatment — the commonest cause of secondary insufficiency.
The second theme is adrenal crisis: a patient in shock that does not respond to fluids and vasopressors, sometimes after an infection, surgery or stopping steroids. Here the correct step is to draw blood for cortisol and ACTH and immediately give hydrocortisone 100 mg intravenously with fluids, without waiting. Further questions: high-dose hydrocortisone also covers the mineralocorticoid need, so fludrocortisone is added only later, in maintenance for primary insufficiency; "sick day rules" — doubling the dose with fever; and in a patient with both hypothyroidism and adrenal insufficiency, steroids are given first and levothyroxine only afterwards.
Key points
- Primary: high ACTH, hyperpigmentation, hyperkalaemia and salt craving.
- Diagnosis: ACTH stimulation test, peak cortisol below 18 µg/dL.
- Crisis: hydrocortisone 100 mg intravenously and fluids at once, without waiting for results.
- Maintenance: hydrocortisone 15–25 mg a day, plus fludrocortisone in primary disease.
- Sick day rules: double the dose with fever and keep an injection kit at home.
Summary table
| Feature | Primary (Addison) | Secondary / tertiary | Exam note |
|---|---|---|---|
| ACTH | High | Low or normal | High ACTH = hyperpigmentation |
| Aldosterone | Lacking: hyperkalaemia, salt craving | Preserved: no hyperkalaemia | Hyponatraemia can occur in both |
| Causes | Autoimmune, tuberculosis, adrenal haemorrhage (anticoagulants, meningococcal sepsis) | Steroid withdrawal, pituitary tumour | Check antibodies to 21-hydroxylase |
| Diagnosis | ACTH stimulation: peak cortisol below 18 µg/dL | Same test; pituitary MRI | Morning cortisol below 5 µg/dL is highly suspicious |
| Maintenance | Hydrocortisone 15–25 mg a day + fludrocortisone | Hydrocortisone only | Double the dose with fever, injection kit |
| Crisis | Hydrocortisone 100 mg intravenously, then 200 mg a day | Same treatment | Saline 1 litre in the first hour |
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Sources
- Endocrine Society Clinical Practice Guideline: Diagnosis and Treatment of Primary Adrenal Insufficiency, 2016 — Diagnosis, replacement therapy and adrenal crisis
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Disorders of the Adrenal Cortex: Adrenal Insufficiency
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.