What is the thyroid gland?
Thyroxine (T4), a major thyroid hormone, is produced by the thyroid gland, which is located near the trachea. Thyroid hormones have wide-ranging effects on the body because they regulate metabolic rate.TSH (thyroid stimulating hormone) is a hormone produced by the pituitary gland, which is located at the base of the brain and regulates thyroid gland function.
What is thyroid testing?
A thyroid test is a blood test that assesses the function of the thyroid gland. 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 ruling out 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 is thyroid testing done in dogs?
To perform a thyroid test, a blood sample is drawn, placed in a special glass tube, and separated into two parts: serum and blood clot. The serum is removed and sent to a laboratory for analysis, while the blood clot is discarded. Although some veterinary hospitals can perform thyroid tests in-house, the majority rely on third-party laboratories.
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 following are some of the most common thyroid tests done for dogs.
T4 & T3
Dogs can be tested for hypothyroidism using total T4 (thyroxine) and total T3 (triiodothyronine) levels. T3 and T4 concentrations can be affected by several variables including medications, disease states, and nutrition. Unexpectedly high levels of either hormone may be a sign of autoantibodies.
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 sick 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 industry-recognized test for canines, requiring an overnight incubation in buffer and dialysis cells to separate bound T4 from free T4. Compared to the ED method, the Immulite method is quicker and less expensive and yields outcomes similar to those of dialysis. Any dog known to have thyroid autoantibodies or suspected of having them should have their thyroid supplementation checked using the FT4 test because it neutralizes the effects of the autoantibodies.
Thyroglobulin Autoantibody (TgAA) Test
TgAA is a canine-specific test used to detect autoimmune thyroiditis. It should be used in conjunction with other thyroid tests for a more accurate diagnosis. Thyroglobulin autoantibodies play a role in the production of T4 and T3.
TSH (thyroid stimulating hormone) can be measured in dogs. High levels of endogenous thyroid-stimulating hormone in dogs suggest hypothyroidism, but normal or low levels do not necessarily rule it out. This test should be used in conjunction with other thyroid tests to make a diagnosis.