Addison’s disease and Cushing’s syndrome are mirror images of each other, and that is exactly why the NCLEX loves to test them together. Addison’s is too little cortisol (and too little aldosterone) — so sodium drops, potassium climbs, glucose falls, and blood pressure tanks. Cushing’s is too much cortisol — so potassium drops, glucose rises, blood pressure goes up, and sodium runs normal to high-normal (frank hypernatremia is uncommon). Lock in the cortisol direction first, and every other finding falls out of it.
What is the core difference between Addison’s and Cushing’s?
Both conditions come down to one hormone: cortisol. Addison’s disease is primary adrenal insufficiency — the adrenal cortex is destroyed and stops making enough cortisol and aldosterone. Cushing’s syndrome is the opposite problem: cortisol excess, most often because someone is taking corticosteroids.
The single best way to keep these straight on exam day is to anchor on cortisol, then reason out the rest. Cortisol raises blood sugar and supports blood pressure. Aldosterone holds onto sodium and dumps potassium. So when cortisol and aldosterone are low (Addison’s), you get low sodium, high potassium, low glucose, and hypotension. When cortisol is high (Cushing’s), you get low potassium, high glucose, and hypertension, with sodium typically normal to high-normal rather than frankly elevated. Same axis, opposite directions.
Addison’s vs Cushing’s discriminator table
The lab and electrolyte rows are the most-tested — and they flip cleanly between the two. Memorize this block first.
| Feature | Addison’s disease (cortisol LOW) | Cushing’s syndrome (cortisol HIGH) |
|---|---|---|
| Sodium (Na⁺) | Hyponatremia — LOW (aldosterone deficit wastes Na) | Normal to high-normal (cortisol/steroid effect retains Na, but frank hypernatremia is uncommon) |
| Potassium (K⁺) | Hyperkalemia — HIGH (no aldosterone to excrete K) | Hypokalemia — LOW (excess steroid drives K out) |
| Glucose | Hypoglycemia — LOW (no cortisol to raise glucose) | Hyperglycemia — HIGH (cortisol is a stress/glucose-raising hormone) |
| Blood pressure / volume | Hypotension, volume depletion, dizziness | Hypertension, fluid retention, edema |
| Cortisol level | Deficient (primary adrenal failure) | Excess |
| Aldosterone | Deficient (primary adrenal — affects both layers) | Normal to suppressed — but excess cortisol itself acts on mineralocorticoid receptors, so Na is retained and K is wasted |
| Skin / appearance | Bronze hyperpigmentation (from high ACTH), weight loss, fatigue, salt craving, nausea/GI upset | Moon face, buffalo hump, truncal obesity with thin arms/legs, purple striae, thin easily-bruised skin, hirsutism |
| Weight | Loss, anorexia | Gain (central/truncal) |
| Mood / mental status | Fatigue, weakness, depression, irritability | Mood swings, emotional lability, sometimes psychosis or euphoria |
| Common causes | Primary Addison’s: autoimmune adrenal destruction (most common), TB. Note: abrupt corticosteroid withdrawal does NOT cause primary Addison’s — it precipitates an adrenal crisis through secondary/tertiary insufficiency (suppression of the HPA axis), so it is a crisis trigger, not a cause of the disease itself. | EXOGENOUS corticosteroids (most common overall), pituitary adenoma (Cushing’s disease), adrenal tumor, ectopic ACTH |
| Life-threatening crisis | Addisonian (adrenal) crisis — profound hypotension/shock, severe hyperkalemia, hypoglycemia. Medical emergency. | No single acute “crisis” equivalent; risks come from chronic HTN, hyperglycemia, infection, osteoporosis, GI bleed |
| Treatment | Lifelong glucocorticoid + mineralocorticoid (fludrocortisone); stress-dose steroids when ill, injured, or surgical | Taper/stop exogenous steroids; surgery for pituitary or adrenal tumor; treat underlying source |
Why do the electrolytes flip?
Addison’s: low cortisol AND low aldosterone
Addison’s is primary adrenal insufficiency, which means the adrenal cortex itself is failing. That matters because the cortex makes both cortisol (the glucocorticoid layer) and aldosterone (the mineralocorticoid layer). Lose aldosterone and the kidney can no longer hold onto sodium or excrete potassium — so sodium spills into the urine (hyponatremia) and potassium backs up in the blood (hyperkalemia). Lose cortisol and you lose your defense against low blood sugar (hypoglycemia) and your vascular tone, which contributes to the hypotension. The high ACTH that the pituitary pumps out trying to flog the dead adrenal gland is what drives the classic bronze hyperpigmentation — a fingerprint of primary Addison’s.
Cushing’s: too much cortisol
Cushing’s is the flood. Excess cortisol acts on the kidney to retain sodium and water (hypertension, edema) while wasting potassium (hypokalemia); sodium typically runs normal to high-normal rather than frankly elevated, because water is retained along with it. Cortisol is a counter-regulatory, glucose-raising hormone, so chronic excess produces hyperglycemia. It also breaks down protein and redistributes fat centrally — hence the moon face, buffalo hump, truncal obesity with spindly extremities, thin skin, easy bruising, and purple striae where stretched skin tears. Notice this is the exact opposite electrolyte and pressure profile of Addison’s.
A memory hook that holds up
Think “Addison’s = Add salt, lose pressure” — patients crave salt, run low sodium, and bottom out their blood pressure. For Cushing’s, picture the swollen “Cushion” — puffy, fluid-overloaded, high pressure, high sugar. Once you fix the direction of cortisol, the sodium, potassium, glucose, and pressure all follow.
Recognizing addisonian crisis
This is the emergency the NCLEX cares about most on the Addison’s side. An addisonian (adrenal) crisis is acute, severe cortisol deficiency (plus aldosterone deficiency in primary Addison’s), often triggered by infection, trauma, surgery, or abruptly stopping steroids. The patient presents with profound hypotension and shock, severe hyperkalemia, and hypoglycemia, frequently with nausea, vomiting, abdominal pain, and fever.
Treatment is immediate and predictable: IV hydrocortisone, aggressive isotonic IV fluids (0.9% sodium chloride to restore volume and sodium), and correction of glucose and potassium. The wrong answer trap here is anything that delays steroids or treats only the blood pressure with fluids alone — the patient needs cortisol replaced. Teach every Addison’s patient to carry an emergency hydrocortisone injection and a medical-alert ID, and to increase their steroid dose during illness or stress rather than skip it.
Diagnosis and treatment essentials
Addison’s is confirmed with a low cortisol that fails to rise after an ACTH (cosyntropin) stimulation test, because the failed adrenal gland cannot respond. Treatment is lifelong replacement — a glucocorticoid (such as hydrocortisone or prednisone) plus a mineralocorticoid (fludrocortisone) to replace the missing aldosterone. The teaching that earns points: never abruptly stop steroids, take stress doses when sick or before surgery, and recognize the early signs of crisis.
Cushing’s work-up looks for failure to suppress cortisol — elevated late-night salivary cortisol, elevated 24-hour urinary free cortisol, and a dexamethasone suppression test that does not suppress. Treatment depends on the cause: if it is exogenous steroids (by far the most common cause overall), the cortisol excess is tapered down carefully — never stopped cold, which could itself trigger an addisonian-type crisis. Pituitary adenomas and adrenal tumors are removed surgically. Until cortisol normalizes, watch for hyperglycemia, hypokalemia, hypertension, infection risk, and fragile skin.
Sample NCLEX questions
1. A client with Addison’s disease is admitted with weakness, hypotension, and nausea. Which set of laboratory values would the nurse most expect?
- Sodium 150 mEq/L, potassium 3.0 mEq/L, glucose 220 mg/dL
- Sodium 128 mEq/L, potassium 5.8 mEq/L, glucose 58 mg/dL
- Sodium 142 mEq/L, potassium 4.0 mEq/L, glucose 95 mg/dL
- Sodium 135 mEq/L, potassium 5.6 mEq/L, glucose 240 mg/dL
Show answer & rationale
Correct answer: B. Addison’s is low cortisol and low aldosterone, producing hyponatremia, hyperkalemia, and hypoglycemia — exactly the pattern in B. Option A points in the opposite, cortisol-excess direction (high Na, low K, high glucose). Option C is all normal values. Option D mixes a high potassium with a high glucose, which does not fit the cortisol-deficient picture (low glucose is expected in Addison’s).
2. A nurse is caring for a client with suspected addisonian crisis. Which prescription should the nurse anticipate implementing FIRST?
- Administer IV hydrocortisone and 0.9% sodium chloride
- Restrict IV fluids to prevent fluid volume overload
- Administer the client’s oral fludrocortisone with breakfast
- Administer IV regular insulin to lower the blood glucose
Show answer & rationale
Correct answer: A. Addisonian crisis is life-threatening cortisol deficiency with hypotension, hyperkalemia, and hypoglycemia; the priority is IV hydrocortisone plus isotonic fluid resuscitation. Oral fludrocortisone (C) is far too slow for an emergency. Restricting fluids (B) is dangerous in a volume-depleted, hypotensive client. Insulin (D) is wrong because the emergency is corrected with IV hydrocortisone plus isotonic fluids, not glucose lowering — and these clients are already hypoglycemic, so insulin would push the blood sugar even lower. (Insulin does shift potassium into cells, but the hyperkalemia of addisonian crisis typically improves once IV hydrocortisone and saline are given, and insulin here would worsen the existing hypoglycemia.)
3. A client with Cushing’s syndrome is being assessed by the nurse. Which findings are consistent with the diagnosis? Select all that apply.
- ☐ Truncal obesity with thin extremities
- ☐ Hyperpigmentation (bronzing) of the skin
- ☐ Purple abdominal striae
- ☐ Hyperglycemia
- ☐ Hyperkalemia
- ☐ Hypertension
Show answer & rationale
Correct answers: Truncal obesity with thin extremities, Purple abdominal striae, Hyperglycemia, Hypertension. These all reflect cortisol excess. Hyperpigmentation is the classic Addison’s finding (driven by high ACTH), not a typical Cushing’s finding. Hyperkalemia is also an Addison’s finding — Cushing’s causes hypokalemia because excess steroid wastes potassium.
4. A client takes high-dose prednisone long-term for an autoimmune disorder and now shows a moon face, central weight gain, and a blood pressure of 158/96. Which statement reflects correct teaching?
- “Stop the prednisone immediately so these changes can begin to reverse.”
- “These changes are signs that you have developed Addison’s disease.”
- “You should double your prednisone dose to control your blood pressure.”
- “Never stop the prednisone on your own; it must be tapered slowly.”
Show answer & rationale
Correct answer: D. Exogenous corticosteroids are the most common cause of Cushing’s-type features, and the management is a supervised taper — never an abrupt stop, which can trigger an addisonian-type adrenal crisis because the body’s own adrenal production has been suppressed. The features point to cortisol excess (Cushing’s), not Addison’s (B). Increasing the dose (C) worsens the excess. Stopping cold (A) is dangerous.
Key takeaways
- Addison’s = cortisol LOW (plus aldosterone low): hyponatremia, hyperkalemia, hypoglycemia, hypotension.
- Cushing’s = cortisol HIGH: hypokalemia, hyperglycemia, hypertension, with sodium normal to high-normal (frank hypernatremia uncommon). Largely the mirror image of Addison’s.
- Bronze hyperpigmentation = Addison’s (high ACTH). Moon face, buffalo hump, truncal obesity, purple striae = Cushing’s.
- Addison’s most common cause = autoimmune adrenal destruction. Cushing’s most common cause overall = exogenous corticosteroids.
- Addisonian crisis is the emergency: hypotension/shock, severe hyperkalemia, hypoglycemia → IV hydrocortisone + isotonic fluids, correct glucose and potassium.
- Never stop steroids abruptly in either direction — Addison’s patients need stress-dose increases when ill; Cushing’s from steroids must be tapered.
- Addison’s treatment = lifelong glucocorticoid + mineralocorticoid (fludrocortisone). Cushing’s treatment = remove the source (taper steroids or resect a tumor).
Frequently Asked Questions
What is the easiest way to remember Addison’s vs Cushing’s labs?
Anchor on cortisol direction. Addison’s is low cortisol and low aldosterone, so you lose sodium (hyponatremia), retain potassium (hyperkalemia), drop glucose (hypoglycemia), and lose blood pressure. Cushing’s is high cortisol, so it largely flips: low potassium, high glucose, high blood pressure, with sodium normal to high-normal (frank hypernatremia is uncommon). A handy hook: “Addison’s — Add salt, lose pressure.”
Why does Addison’s cause hyperpigmentation but Cushing’s does not?
In primary Addison’s the adrenal gland fails, so the pituitary releases very high levels of ACTH trying to stimulate it. That excess ACTH stimulates skin pigmentation, producing the classic bronze tone. Cushing’s from exogenous steroids actually suppresses ACTH, so that bronzing is not part of the typical Cushing’s picture.
What causes addisonian crisis and how is it treated?
An addisonian (adrenal) crisis is acute, severe cortisol deficiency, often triggered by infection, surgery, trauma, or abruptly stopping steroids. The patient develops profound hypotension and shock, severe hyperkalemia, and hypoglycemia. Treatment is emergent: IV hydrocortisone, isotonic 0.9% sodium chloride to restore volume and sodium, and correction of glucose and potassium.
What is the difference between Cushing’s syndrome and Cushing’s disease?
Cushing’s syndrome is the umbrella term for any state of cortisol excess, whatever the cause — most commonly exogenous corticosteroids. Cushing’s disease is one specific cause: a pituitary adenoma that secretes excess ACTH, which then drives the adrenal glands to overproduce cortisol.
Why should you never stop corticosteroids abruptly?
Long-term steroid use suppresses the body’s own cortisol production. Stopping suddenly leaves the patient without enough cortisol from either source, which can trigger an acute adrenal (addisonian-type) crisis. Steroids must be tapered gradually so the adrenal glands can resume their own production.
Keep practicing
Addison’s and Cushing’s are easiest to master alongside the rest of the adrenal and endocrine picture. Work through the full NCLEX endocrine review, then drill the other classic mirror-image pair on the hypothyroidism vs hyperthyroidism comparison. Brushing up on normal lab values and fluid and electrolyte balance will make the sodium and potassium shifts click even faster.
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- NIDDK - Cushing's Syndrome — Exogenous glucocorticoids are the most common cause; UFC, late-night saliva, dexamethasone tests
- NIDDK - Adrenal Insufficiency & Addison's Disease: Symptoms & Causes — Autoimmune causes most Addison's; skin darkening, salt craving, hypotension, hypoglycemia
- NIDDK - Adrenal Insufficiency & Addison's Disease: Treatment — Hydrocortisone + fludrocortisone; crisis treated with IV corticosteroids and IV saline
- NIDDK - Adrenal Insufficiency & Addison's Disease: Diagnosis — ACTH stimulation test is the test used most often to diagnose adrenal insufficiency
- Endocrine Society - Diagnosis and Treatment of Primary Adrenal Insufficiency guideline (JCEM) — Crisis: hydrocortisone 100 mg IV + 1 L isotonic saline; injection kit, steroid card, alert ID
Sources checked September 2026.