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My dog has low thyroid and is losing weight. Is it serious?

Updated On September 23rd, 2025

Pet's info: Dog | German Spitz | Male | unneutered | 12 lbs

My dog had a blood test has a slightly low thyroid level. he has last a good deal of weight. He has no other symptoms at all. He is happy.. eats. . No pain or trouble with functions. The vet found no lumps anywhere. I'm struggling to get clear advice from the vet. I can't afford the referral cost for mri. What are the chances it's serious. My vet just won't give me any indication and I'm in bits with worry.

2 Answers

Most Helpful Answer

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Answered By Jenna Beyer, DVM, MBA, cVMA

Veterinarian, Certified Veterinary Acupuncturist

Published on August 11th, 2017

If you have a copy of Milo's medical record, you can choose a Petco Pet Education Center, formerly Petcoach Consult to discuss this fully. Hypothyroidism does not usually cause weight loss in dogs, and the test may be caused by euthyroid sick syndrome, meaning the thyroid hormone is low because of some other illness. There are confirmatory tests that can help your vet decide if Milo needs to be on thyroid therapy. If there are no other abnormalities on a CBC and complete blood chemistry, then additional diagnostics may be indicated, including intestinal parasite screen, GI panel, x-rays, abdominal ultrasound, etc. If Milo has a good appetite without vomiting or diarrhea, you could try feeding more calories. I like Purina ProPlan Sport. You could also try puppy food, which is higher in fat. If you do decide to switch food, mix them together slowly over 2-3 weeks to avoid an upset stomach.

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    Answered By Rebecca, DVM

    Veterinarian

    Published on August 12th, 2017

    I'm sorry if my answer wasn't clear. Low thyroid when it isn't primary thyroid disease is called "euthyroid sick" it means the thyroid gland is normal but something else is abnormal. Almost anything can cause this- chronic illness, viral infection, anorexia. A low level of thyroid hormone is not a very specific sign unless related directly to thyroid disease. So as far as that result goes I would not consider it very significant or serious

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