Thyroid (T4) testing explained
Thyroid disease runs opposite in dogs and cats: dogs get hypothyroidism (low T4), cats get hyperthyroidism (high T4). T4 is the first screening step; abnormal results usually need a recheck or free T4/TSH.
🧾 Before the test
- ✓No fasting needed
- ✓Mention medications that can affect the result
📊 Reading the key values
| Search | High | Low |
|---|---|---|
| Dog T4 | Rare (thyroid tumor or over-supplementation) | Hypothyroidism: weight gain, symmetrical hair loss, low energy — but non-thyroid illness also lowers T4, confirm with free T4/TSH |
| Cat T4 | Hyperthyroidism: ravenous appetite with weight loss, vomiting, fast heart — the core senior-cat screen | Rare |
💡 How to read it A single low T4 in a dog is not proof of hypothyroidism (other illness falsely lowers it). A raised T4 in a cat largely confirms hyperthyroidism. Both are treatable with good long-term outlooks.
🤖 AI report interpretation
Type the values from your report below (e.g. “ALT 250, BUN 40”) and the AI will interpret them against each test’s reference meanings.
FAQ
Is hypothyroid medication lifelong?
Usually yes. Levothyroxine is inexpensive; after dose adjustments most dogs do very well.
How is feline hyperthyroidism treated?
Four options: anti-thyroid drugs, prescription iodine-restricted food, radioactive iodine therapy (curative), or surgery. Discuss trade-offs with your vet.