The diagnosis and management of thyroid diseases in dogs need valid testing for it to be accurate. Today, our Tigard vets discuss what thyroid testing is, how thyroid testing is done, and some common types of tests.
What is the thyroid gland?
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 because they regulate metabolic rates. The pituitary gland, located at the base of the brain, regulates thyroid gland function with a hormone known as TSH (thyroid stimulating hormone).
What is thyroid testing?
A thyroid test is a blood test that determines the function of the thyroid gland. It is advised in any sick animal and is commonly used as a screening test for underlying illness or disease. Normal results help determine health and rule out specific 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 is thyroid testing done in dogs?
Blood must be drawn for a thyroid test, divided into serum and blood clot, and then put in a special glass tube. The blood clot is discarded while the serum is removed and sent to a lab for analysis. While some veterinary hospitals have their own laboratories, the majority rely on outside labs to perform thyroid tests.
If performed at the veterinary hospital, a thyroid test usually takes about 40–60 minutes. If given to an outside laboratory, you can expect the results within 1–2 days.
Most dogs do not require sedation or anesthesia. Some dogs, however, dislike needles and may require anesthesia.
What are some common types of thyroid tests?
The most typical thyroid tests for dogs include the ones listed below.
T4 & T3
Dogs can be tested for hypothyroidism using total T4 and total T3 (thyroxine and triiodothyronine) levels. T3 and T4 concentrations can be affected by a variety of factors including medications, disease states, and nutrition. Unusually high levels of either hormone may be an indication of autoantibodies.
Free T4 by lmmulite or by Equilibrium Dialysis
A reliable assay for measuring free T4 (FT4) can distinguish true hypothyroidism from the euthyroid sick state. The concentration of non-protein bound thyroxine, FT4, in the blood, is lower than that of total T4. For accurate FT4 testing, a method should be used to separate the protein-bound hormone from the free (unbound) hormone.
The Equilibrium Dialysis (ED) method is the gold standard for dogs and requires 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, yielding results similar to dialysis. Thyroid supplementation in any dog known or suspected to have thyroid autoantibodies should be monitored using FT4, as these tests remove the autoantibody effects.
Thyroglobulin Autoantibody (TgAA) Test
The TgAA test is a dog-specific thyroid 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.
The endogenous thyroid stimulating hormone (TSH) can be measured in dogs. High levels of endogenous thyroid-stimulating hormone levels suggest hypothyroidism, but normal or low endogenous thyroid-stimulating hormone levels in dogs do not necessarily rule it out. This test should be used in conjunction with other thyroid tests to make a diagnosis.