NAVLE clinical reasoning guide
Addison's disease
Hypoadrenocorticism · high exam frequency · internal medicine + emergency overlap
Build the decision, one step at a time
Use the reasoning path to move from the presenting pattern to the next best action.
Recognize
Identify the urgent pattern and the clues that should control your first decision.
Exam core — read this first
Sick dog + bradycardia → think Addison's
Crisis first → collapsed, hypotensive, bradycardic dog gets 0.9% NaCl before confirmatory testing
Stable patient → ACTH stimulation test
Safe steroid before testing → dexamethasone only
Emergency Triage Alert
Crisis First: Stabilize Before You Confirm
A collapsed, hypotensive, bradycardic dog is an emergency first and an endocrine workup second. Start 0.9% NaCl immediately; use dexamethasone if a steroid is needed before ACTH stimulation testing.
Monitoring Note
Secondary Monitoring
Addison's is not zoonotic, but chronic mineralocorticoid deficiency requires consistent electrolyte monitoring to prevent crisis.
Pattern recognition
Core pattern
Sick dog + bradycardia
Collapse / weakness
Vomiting + diarrhea
Supporting clues
Waxing / waning history
Weight loss
Pale or tacky mucous membranes
Young–middle-aged female
Shaking or muscle weakness
NAVLE trigger: The mismatch is the signal. Very sick dogs are usually tachycardic. If the patient looks shocked but the heart rate is slow, think hyperkalemia and push Addison's high on the list.
Differentiate
Separate the closest look-alikes before committing to a diagnosis or treatment lane.
Differentials — how to separate these on NAVLE
Fast separator: Addison's is the one that gives you a very sick dog with bradycardia. Most other collapse or shock differentials are normal heart rate or tachycardic.
| Disease | Heart rate | Na:K ratio | Key separator |
|---|---|---|---|
| Addison's (typical) | ↓ Bradycardia | < 27 | Bradycardia + low Na:K |
| Addison's (atypical) | ↓ Bradycardia | Normal | Normal electrolytes do not exclude it |
| Trichuris vulpis (whipworms) | Normal / ↑ | Can be low | Pseudo-Addison mimic with GI parasite history |
| Postrenal urinary obstruction | ↓ possible | Variable / K high | Stranguria, anuria, large painful bladder, postrenal azotemia |
| Chronic kidney disease | Normal / ↑ | Normal | Dilute urine / loss of concentrating ability |
| Primary GI disease | Normal / ↑ | Normal | No classic electrolyte pattern |
| Septic shock | ↑ Tachycardia | Normal | Fever, source, tachycardia |
Diagnose
Choose the next best test or interpretation based on stability and the leading clinical pattern.
Decision core — what NAVLE actually asks
Unstable patient — hypotensive, obtunded, bradycardic
→ IV fluid resuscitation first (0.9% NaCl) · do NOT delay for diagnostics · stabilize before anything else
Stable patient — weak, GI signs, abnormal labs
→ Proceed to ACTH stimulation test to confirm diagnosis · then start appropriate therapy
Stable patient with normal electrolytes but high suspicion
→ Do not rule out atypical Addison's · run ACTH stimulation testing and monitor for later mineralocorticoid deficiency
Safe steroid if giving before ACTH test
→ Use dexamethasone only — it is NOT detected by cortisol assay and will not invalidate the test
Severe hyperkalemic arrhythmia present
→ Continue aggressive stabilization and use IV calcium gluconate for cardioprotection
Key interpretation
Sodium
↓ Low
Aldosterone deficiency → Na wasting
Potassium
↑ High
K retention → bradycardia risk
Na:K ratio
< 27
Classic high-yield pattern
Glucose
May be low
Correct hypoglycemia if present
Azotemia
Prerenal
From hypovolemia — not primary renal failure
CBC
No stress leukogram
Normal/increased lymphocytes or eosinophils in a sick dog support Addison's
Urine SG
Normal / not dilute
Helps separate from CKD
ACTH stim
Flat cortisol response
Definitive confirmation
⚠ Normal potassium does NOT rule out Addison's disease. Electrolytes may be normal initially, and these patients still require monitoring because mineralocorticoid deficiency can develop later.
Treat
Connect stabilization and treatment choices to the clinical state, then check the common exam traps.
Treatment
Acute
0.9% NaCl IV bolus + dexamethasone sodium phosphate IV
Stabilize hemodynamics first. Dexamethasone is safe before ACTH testing, and correct hypoglycemia if present.
Rhythm
IV calcium gluconate if severe hyperkalemic arrhythmias are present
This is for cardioprotection while definitive stabilization continues.
Chronic
DOCP (Percorten-V) every 25–30 days + daily prednisone
DOCP = mineralocorticoid replacement · prednisone = glucocorticoid replacement.
Alt.
Fludrocortisone acetate twice daily + prednisone
Alternative option. Usually needs more dose adjustment over time.
Monitor
Recheck electrolytes, renal values, hydration, clinical energy, and glucocorticoid/mineralocorticoid balance
Chronic management is adjusted to the patient; stable electrolytes and clinical response are the goal.
Pharmacology pearls
DOCP (Percorten-V)
Logic: Replaces aldosterone
Board Pearl: Given IM/SC every ~25-30 days; only affects electrolytes, NOT cortisol.
Fludrocortisone
Logic: Dual replacement
Board Pearl: Oral daily dosing; often requires more frequent electrolyte monitoring than DOCP.
Dexamethasone
Logic: Acute stabilization
Board Pearl: Safe to give BEFORE ACTH stim; does not cross-react with cortisol assay.
NAVLE traps — where students lose marks
Bradycardia in a sick dog is not normal
This is the main red flag. Shocked dogs are usually tachycardic — bradycardia points to hyperkalemia and Addison's.
Do NOT wait for ACTH results before starting IV fluids in an unstable patient
Stabilization comes first. Diagnosis follows once the patient is safe.
Normal potassium does NOT rule out Addison's disease
Atypical Addison's can present with normal electrolytes. Clinical suspicion still matters.
Whipworms can create a pseudo-Addison electrolyte pattern
Trichuris vulpis is a classic board-style mimic when the sodium and potassium pattern looks convincing.
Postrenal obstruction can mimic hyperkalemic Addison's
A blocked dog can be bradycardic with hyperkalemia and azotemia. Check urination history and bladder size before anchoring.
Prednisone before ACTH stimulation test will interfere with results
Use dexamethasone instead. Prednisone cross-reacts with cortisol assays.
Na:K ratio is supportive, not definitive
Low Na:K should raise suspicion, but obstruction, whipworms, severe GI disease, and renal disease can mimic parts of the pattern.
Missing the no-stress-leukogram clue
A sick dog without the expected stress leukogram supports cortisol deficiency and should strengthen suspicion.
Apply the decision
Pre-built NAVLE-style · Addison's disease. One question is shown at a time.
Question 1 of 5
0 correct
A 4yr FS Standard Poodle presents with acute collapse, vomiting, and profound weakness. On examination, the dog is depressed and poorly perfused, but the heart rate is only 48 bpm. Which diagnosis should rise sharply on your differential list?
A 5yr MN Standard Poodle presents collapsed and obtunded. HR is 44 bpm, BP 65/40 mmHg. The owner reports intermittent vomiting for one week. Bloodwork is pending. Which of the following is the most appropriate immediate next step?
A 6yr MN mixed-breed dog presents for collapse and vomiting. HR is 52 bpm, pulses are weak, potassium is 7.2 mmol/L, sodium is mildly decreased, and creatinine is elevated. The owner says he has been straining to urinate all morning, and palpation reveals a large painful bladder. Which interpretation best prevents a NAVLE anchoring error?
A dog strongly suspected of atypical Addison's has normal sodium and potassium today. Which statement is most accurate?
A 6-year-old dog has chronic waxing and waning vomiting, weight loss, weakness, mild hypoglycemia, and no stress leukogram. Sodium and potassium are currently normal. Which next step best matches Addisonian diagnostic reasoning?
Fast review
Use this after practice to recall the highest-yield decisions without rereading the full guide.
30-second revision
Key trigger signSick dog + bradycardia
Key labsNa↓ K↑ Na:K < 27
First step (unstable)IV fluids — 0.9% NaCl
Safe steroid pre-testDexamethasone only
CBC pearlSick dog without stress leukogram
Confirm diagnosisACTH stimulation test
Chronic RxDOCP + prednisone
Critical trapNormal K ≠ rules out Addison's
Mechanism, tools, and related topics
Clinical mechanism — only what matters
↓ Aldosterone → Na loss + K retention → hypovolemia + bradycardia
↓ Cortisol → poor stress response → collapse under stress
You do not need deeper pathophysiology here. Just know how the hormone deficits create the clinical clues NAVLE tests.
Clinical application tools
Use these only as support. They reinforce the real management logic for Addisonian patients.
Related topics