Hypothyroidism
The thyroid glands sit on either side of the neck in dogs and cats, and these glands are responsible for maintaining normal metabolic rates. With hypothyroidism, which is the most common endocrine disease in dogs, the thyroid glands stop producing thyroid hormones which leads to a variety of problems.
The classic hypothyroid dog is a middle aged, overweight dog that seems to have slowed down within the past year or so. A lot of owner will attribute this to the dog aging, but sometimes it is just a lack of thyroid hormone causing the symptoms. Hypothyroid dogs commonly also have recurrent skin problems, hair loss (especially on the tail and hips), ear infections, and dry or coarse coats. They can have abnormal heart rhythms on physical exams. Blood tests can also show anemia and high cholesterol levels.
Hypothyroidism can be diagnosed by blood testing. There are several tests we can choose from when trying to diagnose hypothyroidism in our patients. These include T4 testing, T4/TSH testing, and FT4 testing.
When a patient is diagnosed with hypothyroidism, they are started on thyroid hormone supplements. These supplements are given twice daily for the rest of the dog's life. Typically, dogs respond well within 30-60 days, gaining energy, starting to lose weight, and their secondary problems begin to improve. We like to recheck a T4 level 30 days after starting thyroid supplementation to make sure the medication levels are within normal limits. Then we recheck this T4 level on a yearly basis or as needed thereafter. Dogs with hypothyroidism, if properly supplemented, can lead normal, healthy lives, but they may occasionally have flare-ups from secondary skin or ear problems that need to be addressed as they arise.
The classic hypothyroid dog is a middle aged, overweight dog that seems to have slowed down within the past year or so. A lot of owner will attribute this to the dog aging, but sometimes it is just a lack of thyroid hormone causing the symptoms. Hypothyroid dogs commonly also have recurrent skin problems, hair loss (especially on the tail and hips), ear infections, and dry or coarse coats. They can have abnormal heart rhythms on physical exams. Blood tests can also show anemia and high cholesterol levels.
Hypothyroidism can be diagnosed by blood testing. There are several tests we can choose from when trying to diagnose hypothyroidism in our patients. These include T4 testing, T4/TSH testing, and FT4 testing.
- T4- this is measured thyroid hormone that is found bound to proteins within the blood stream. In dogs with hypothyroidism, T4 levels will be low because the thyroid gland is damaged. This is the test we normally run on routine bloodwork screenings in our middle aged and older patients, looking for possible hypothyroidism in dogs with no clinical symptoms. T4 levels, however, can be falsely lowered from concurrent diseases and from certain medications without the dog having true hypothyroidism. This is why we often run either a T4/TSH panel or a FT4 level instead when we suspect a dog has hypothyroidism.
- T4/TSH - TSH is thyroid stimulating hormone, and it is released from the pituitary gland in the brain in response to low blood levels of thyroid hormone. It acts on the thyroid gland to stimulate more thyroid hormone to be released. In dogs with hypothyroidism (suggested by a low T4 level) TSH levels will be high because the pituitary is trying to stimulate the thyroid gland to work. Dogs with normal TSH and low T4 are not truly hypothyroid - there is another disease process with is falsely lowering the blood levels of T4. Also, about 20% of dogs will not have elevated TSH levels even if they are truly hypothyroid, so this panel will not catch all cases of hypothyroidism.
- FT4 - this is thyroid hormone that is free within the bloodstream and is not bound to blood proteins. This level of hormone is more tightly regulated than T4 levels and is not affected by concurrent illnesses or medications. This test is usually our first line screening test for dogs we suspect have hypothyroidism.
When a patient is diagnosed with hypothyroidism, they are started on thyroid hormone supplements. These supplements are given twice daily for the rest of the dog's life. Typically, dogs respond well within 30-60 days, gaining energy, starting to lose weight, and their secondary problems begin to improve. We like to recheck a T4 level 30 days after starting thyroid supplementation to make sure the medication levels are within normal limits. Then we recheck this T4 level on a yearly basis or as needed thereafter. Dogs with hypothyroidism, if properly supplemented, can lead normal, healthy lives, but they may occasionally have flare-ups from secondary skin or ear problems that need to be addressed as they arise.