TL;DR

Here’s what I want to share with everyone:

• As dogs get older, regular health checkups really are important!
• If your dog has clinical symptoms, see a vet
• A low tT4 alone doesn’t necessarily mean hypothyroidism. If only tT4 is low with no other clinical symptoms, it’s worth running additional tests to confirm the diagnosis
• If your dog is genuinely diagnosed with hypothyroidism, do not stop medication on your own — always consult your vet first

The (Possible) Misdiagnosis

Our dog Lottery (probably 15 years old now) had a low tT4 reading come up during a routine checkup in 2022. It stayed consistently low across multiple tests.
He had no clinical symptoms at all — well, maybe his skin wasn’t in great shape, but that was the only thing remotely related. His appetite, water intake, and coat were all completely normal.
Even so, the vet recommended we start him on Thyrozine in February, saying he’d need to take it for life and come in regularly to monitor his levels.
So we started the medication, and I posted in a Facebook group about it a couple of weeks in, asking about care and dosing.

But after starting the medication (twice a day, 3.5 pills of Thyrozine each dose), Lottery actually started peeing indoors more, and his water intake went up noticeably. Something felt off. We brought him back in.
The vet found that his tT4 had gone back up above the normal range, but given our concerns, they reduced the dosage to 3 pills per meal. Even at the lower dose, the indoor accidents kept happening.

Getting a Second Opinion

We ended up seeing two more vets over the next while, and in both cases we mentioned that he was currently on Thyrozine for hypothyroidism.

The vet at Mi-En Animal Hospital felt that for an older dog, slightly lower thyroid levels can be a normal part of aging — and that without any clinical symptoms, medication might not be necessary. Unfortunately there wasn’t time to draw blood that day.

We also visited Chung-Hsing Riverside Animal Hospital, where Dr. Tseng shared the same concern and asked whether any other tests had been run beyond tT4.
We didn’t know any better — we’d only been told the tT4 was low.
Dr. Tseng suggested we temporarily stop the medication and come back in a month for a more comprehensive blood panel.
A month later, we drew blood and sent it to an external lab (testing TT4, free T4, and TSH). The results didn’t show a clear picture of hypothyroidism, and the conclusion was that medication wasn’t needed.

So we stopped and just kept an eye on him.
It’s now been more than six months, and his appetite, energy, and coat are all completely normal and healthy 🙂
I’m genuinely so grateful to the vets at Mi-En and Chung-Hsing Riverside for their careful approach 🙂

Diagnosing Hypothyroidism Requires a Comprehensive Panel

Even though six months have passed and everything is fine, I kept wondering whether stopping the medication was really the right call.

Then I listened to this episode of the Super Good Vet podcast, and finally felt that weight lift off my chest:
As it turns out, diagnosing hypothyroidism based on tT4 alone may be moving too fast. The diagnosis may have been premature.

Other veterinary articles have discussed similar situations:

• Diagnosing Canine Hypothyroidism
• Canine Hypothyroidism: The Complete Breakdown

I’m so glad we eventually found careful vets who ran a full panel and confirmed the actual picture.
Thanks to that, Lottery got to go back to living his life without daily medication Q_Q (and we saved quite a bit of money too). I hope this helps someone else in a similar situation!

Thanks for reading :D

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