Today, our Woburn veterinarians talk about how we accurately test for thyroid disease in dogs, including how the testing is done and some common types of tests we use.
Thyroid Gland in Dogs
The thyroid gland, which is located near the trachea, produces thyroxine (T4), a major thyroid hormone. Thyroid hormones have far-reaching effects on the body by regulating metabolic rate. The pituitary gland, located at the base of the brain, regulates thyroid gland function with a hormone called TSH (thyroid stimulating hormone).
Thyroid Testing
A thyroid test is a blood test to check how well an animal's thyroid gland is working. It's often done when an animal is sick to see if there's an underlying health issue. Normal results mean the animal is healthy and doesn't have certain diseases.
If the animal bleeds easily, it's important to be careful after taking the sample to prevent more bleeding from where the sample was taken.
The Testing Process
A thyroid test for dogs involves taking a small blood sample. This sample is put in a special tube and separated into two parts: serum and a blood clot. The serum is sent to a lab for testing, and the blood clot is thrown away.
Some vet hospitals can do this test on-site, which usually takes 40-60 minutes. You'll get results in 1-2 days if it's sent to an outside lab.
Most dogs don't need sedation, but a few who are scared of needles might need anesthesia.
Common Types of Thyroid Testing
The following are some common thyroid tests performed for dogs.
T4 & T3
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 a variety of factors, including medications, disease states, and nutrition, can influence T3 and T4 concentrations.
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.