→ Run routine database, then confirm with a thyroid panel interpreted in context
Hospitalized or systemically ill dog with low total T4
→ Do not diagnose hypothyroidism from that result alone; consider euthyroid sick syndrome or drug effects first
Confirmed primary hypothyroidism
→ Start levothyroxine and recheck a post-pill thyroid value after several weeks
Key interpretation
Total T4
↓ Low
Useful screen only; not specific
Free T4
↓ Low
Better support for true disease
cTSH
↑ High
Supports primary hypothyroidism
Cholesterol
↑ High
Classic supportive clue
CBC
Mild nonregenerative anemia
Common but not specific
Drugs / illness
Can lower T4
Steroids and illness can mislead you
⚠ A low total T4 does not automatically equal hypothyroidism. NAVLE likes the sick-dog low T4 trap.
Treatment
Start
Levothyroxine orally
Dose consistently so interpretation of monitoring is meaningful.
Monitor
Recheck thyroid values 4–6 hours post-pill after 4–8 weeks
Match the number to clinical improvement, not the number alone.
Also
Treat secondary pyoderma / otitis if present
Energy improves earlier than haircoat. Owners should expect that sequence.
NAVLE traps — where students lose marks
✕
Low total T4 alone is not a diagnosis
Illness and drugs can suppress total T4. Boards test whether you know when the screen is misleading.
✕
Do not call every alopecic dog hypothyroid
A very itchy dog with recurrent otitis is more often allergic than hypothyroid.
✕
Obesity alone is not hypothyroidism
The exam pattern needs metabolic plus dermatologic or neuromuscular clues.
✕
Clinical improvement happens in stages
Coat improvement lags behind energy improvement. That is expected early in therapy.
Differentials — how to separate these on NAVLE
Fast separator: True hypothyroidism is a chronic, non-pruritic metabolic + dermatologic syndrome. The exam often contrasts it with sick-dog low T4 and other endocrine look-alikes.
Disease
T4 pattern
Skin pattern
Key separator
Hypothyroidism
Low free T4, often high TSH
Non-pruritic symmetric alopecia
Weight gain + lethargy + hypercholesterolemia
Euthyroid sick syndrome
Low total T4
Variable
Sick patient; thyroid drop is secondary
Hyperadrenocorticism
Usually normal thyroid values
Thin skin, calcinosis
Panting, PU/PD, polyphagia
Chronic allergy / pyoderma
Normal
Usually pruritic
Itch drives the case
Obesity / deconditioning
Normal
Normal
No classic skin or lab pattern
Clinical application tools
These help with baseline interpretation and dose checks. They do not replace choosing the right patient for testing.
A 7yr FS Golden Retriever presents for chronic lethargy, weight gain, and recurrent superficial pyoderma. Examination reveals bilaterally symmetric truncal alopecia. Which diagnosis best fits this pattern?
Correct answer: B. Chronic lethargy, weight gain, and non-pruritic symmetric alopecia with recurrent skin infections is the classic hypothyroid pattern.
Q2Trap interpretation
A hospitalized dog with pneumonia is receiving glucocorticoids. A screening panel shows a low total T4. Which conclusion is most appropriate?
Correct answer: C. This is the euthyroid sick syndrome trap. Illness and glucocorticoids can suppress total T4 without true hypothyroidism.
Q3Next best step
A stable outpatient dog has lethargy, weight gain, bilateral alopecia, and fasting hypercholesterolemia. Which diagnostic plan is most appropriate?
Correct answer: B. This is the right patient to test. Boards want you to confirm appropriately, not jump from pattern straight to treatment.
Q4Monitoring
A dog with confirmed hypothyroidism has been started on levothyroxine. Which follow-up plan is best?
Correct answer: D. Post-pill monitoring after a few weeks is the classic board answer for levothyroxine follow-up.
Q5Trap question
A dog with severe pruritus, recurrent otitis, and self-trauma has a borderline-low total T4 but normal energy and body weight. Which explanation is most likely?
Correct answer: A. Hypothyroidism is usually non-pruritic. A very itchy dog with otitis should push allergy or infection ahead of thyroid disease.
