Health conditions can have an effect on a number of areas of your pet's health, some can even affect hormone production which regulates bodily functions. Here, our Crystal Lake vets talk about the purpose of the thyroid, why it may be necessary to test for low thyroid in dogs, and the different types of tests used.
What is the thyroid gland?
The thyroid gland, which is located near the trachea, produces thyroxine (T4), a major thyroid hormone. The hormones produced by the thyroid gland are in charge of regulating the metabolism of your dog. The pituitary gland, located at the base of the brain, regulates thyroid gland function with a hormone called TSH (thyroid stimulating hormone).
What is a thyroid test for dogs?
If your vet suspects that your dog's thyroid gland isn't producing an adequate amount of the hormone they may recommend a blood test. It is recommended in any sick animal and is frequently used as a screening test for underlying illness or disease. Normal results aid in determining health and excluding certain diseases.
If the animal tends to have excessive bleeding, extra care should be taken after obtaining the sample to ensure no hemorrhaging from the site where the sample was obtained.
How does the vet perform thyroid tests for dogs?
When performing thyroid tests for dogs, your vet will take a blood sample, place it into a glass tube, and use a centrifuge to separate it into its different parts, mainly the blood cells and serum/plasma. The plasma is extracted and sent to a laboratory for testing, while the blood clot is discarded. Some veterinary hospitals can perform thyroid tests in-house, but most rely on outside laboratories.
If performed at the veterinary hospital, a thyroid test usually takes about 40 – 60 minutes. If an external lab is required to read the test results then you can expect to wait at least a day or two for the results.
While sedation and anesthesia may not always be required, some dogs may be more comfortable if they are sedated.
What tests are used to detect dogs with low thyroid levels?
There are a number of different types of diagnostic tests that your vet may use to diagnose thyroid issues. Some of these tests include:
T4 & T3 Hormone Testing
Total T4 (Thyroxine) and Total T3 (Triiodothyronine) testing can be used to screen for hypothyroidism in dogs. Unexpectedly high levels of either hormone may be indicative of autoantibodies, and T3 and T4 concentrations can be influenced by a variety of factors including medications, disease states, and nutrition.
Free T4 Testing
A valid assay for measuring free T4 (FT4) can be used to distinguish true hypothyroidism from euthyroid sick syndrome. 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. This test should be used along with others to confirm diagnosis. Thyroglobulin autoantibodies are involved in the synthesis of T4 and T3.
TSH measurement
The endogenous thyroid stimulating hormone (TSH) can be measured in dogs. High levels of endogenous thyroid-stimulating hormone suggest hypothyroidism, but normal or low endogenous thyroid-stimulating hormone levels in dogs do not necessarily rule it out. Your vet will perform other types of thyroid testing along with this one to ensure accuracy.
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.