Modern medical veterinary technology allows us to accurately test for thyroid disease in dogs. In this post, our Astoria veterinarians explain how this testing is done and list some of the most common types of tests.
The Thyroid Gland in Dogs
Located near the trachea, the thyroid gland produces thyroxine (T4), a major thyroid hormone. Thyroid hormones impact many processes throughout the body by regulating metabolic rate. The pituitary gland is located at the base of the brain and regulates the function of the thyroid gland with a hormone called TSH (thyroid stimulating hormone).
Thyroid Testing
A thyroid test is a type of blood test your vet can perform to assess how well your pet's thyroid gland is working. It's often done when an animal is ill to find out whether there's an underlying health problem. Normal results mean a dog is healthy and doesn't have certain diseases.
If your pet bleeds easily, it's important to be careful after the sample is taken to prevent more bleeding from occurring in the area where the sample was taken.
The Testing Process
A thyroid test for dogs entails taking a small blood sample, which is put in a special tube and separated into two parts: serum and a blood clot. While the serum is sent to a lab for testing, the blood clot is disposed of.
Some veterinary hospitals can perform this test onsite, which usually takes about 40 to 60 minutes. If it's sent to an outside lab, you'll receive the results in one to two days.
Though most dogs don't need to be sedated for this test, a few who are scared of needles may need anesthesia.
Common Types of Thyroid Testing
Here are some common thyroid tests performed for dogs:
T4 & T3
Total T4 (Thyroxine) and Total T3 (Triiodothyronine) testing can be done to screen for hypothryoidism in dogs. If levels of either hormone are unexpectedly high, this may indicate autoantibodies, and many factors, including disease states, nutrition, and medications, can influence concentrations of T3 and T4.
Free T4 By lmmulite or By Equilibrium Dialysis
A valid assay for measuring free T4 (FT4) can be used to distinguish true hypothyroidism from euthyroid condition. The non-protein bound thyroxine, FT4, is found in lower concentrations in the blood than total T4. A method should be used to separate the protein-bound hormone from the free (unbound) hormone for accurate FT4 testing.
The Equilibrium Dialysis (ED) method is the gold standard test for dogs, requiring an overnight incubation in buffer and dialysis cells to separate bound T4 from free T4. The Immulite method is less expensive and faster than the ED method, producing results comparable to dialysis. Thyroid supplementation should be monitored using FT4 in any dog known or suspected to have thyroid autoantibodies, as these tests remove the autoantibody effects.
Thyroglobulin Autoantibody (TgAA) Test
The TgAA test is a canine-specific test for detecting autoimmune thyroiditis. For a more accurate diagnosis, it should be used in conjunction with other thyroid tests. Thyroglobulin autoantibodies are involved in the synthesis of T4 and T3.
TSH measurement
In dogs, we can check their thyroid function using a hormone called TSH. If a dog has high TSH levels, it could mean they have hypothyroidism. However, if a dog has normal or low TSH levels, it doesn't necessarily mean they don't have hypothyroidism. To be sure, it's best to use this test along with other thyroid tests when making a diagnosis.
Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.