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Thyroid Hormone Testing in Dogs

The diagnosis and management of thyroid diseases in dogs need valid testing for it to be accurate. Today, our Poway 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 produces thyroxine (T4), a major thyroid hormone, and is located near the trachea. Regulating metabolic rate, thyroid hormones have extensive effects on the body.TSH, a hormone produced by the pituitary gland at the base of the brain, controls the function of the thyroid gland.

What is thyroid testing for dogs?

The thyroid gland's function can be evaluated through a blood test known as a thyroid test. Using it in any sick animal is highly recommended and it is commonly employed as a screening test for underlying illness or disease. Healthy results help determine one's well-being and rule out specific illnesses.

After obtaining the sample, it is important to take extra care to prevent any bleeding from the site where it was obtained, especially if the animal is prone to excessive bleeding.

How is thyroid testing done in dogs?

To perform a thyroid test, a blood sample is drawn and placed in a special glass tube. The sample is then separated into two parts: serum and blood clot. We extract the serum and send it to a laboratory for testing, while discarding the blood clot. Most veterinary hospitals rely on outside laboratories for thyroid tests, although some can perform them in-house.

A thyroid test typically lasts around 40–60 minutes when conducted at the veterinary hospital. Results from an outside laboratory typically arrive within 1–2 days.

Sedation or anesthesia is not necessary for most dogs. Needles can be unsettling for certain dogs, leading to the need for anesthesia.

What are some common types of thyroid tests?

The following are some of the most common thyroid tests done for dogs.

T4 & T3

Screening for hypothyroidism in dogs can be done using Total T4 (Thyroxine) and Total T3 (Triiodothyronine) testing. Autoantibodies may be indicated by unexpectedly high levels of either hormone. Various factors, such as medications, disease states, and nutrition, can influence the concentrations of T3 and T4.

Free T4 by lmmulite or by Equilibrium Dialysis

You can use a valid assay to measure free T4 (FT4) and differentiate between true hypothyroidism and euthyroid sick condition. Free thyroxine, FT4, is present in the blood at lower levels compared to total T4. Using a method to separate the protein-bound hormone from the free (unbound) hormone is crucial for accurate FT4 testing.

The Equilibrium Dialysis (ED) method is considered the most reliable test for dogs. It involves an overnight incubation in buffer and dialysis cells to separate bound T4 from free T4. The Immulite method offers a more cost-effective and efficient alternative to the ED method, delivering results that are on par with dialysis. Monitoring thyroid supplementation in dogs with known or suspected thyroid autoantibodies should involve the use of FT4 tests, as they effectively eliminate the effects of autoantibodies.

Thyroglobulin Autoantibody (TgAA) Test

The TgAA test detects autoimmune thyroiditis specifically in canines. Using it alongside other thyroid tests will provide a more accurate diagnosis. Thyroglobulin autoantibodies play a role in the production of T4 and T3.

TSH measurement

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.

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.

Do you suspect your dog is suffering from a thyroid issue? Don't hesitate to contact our Poway vets to schedule an appointment today. We can perform an initial blood test or a urinalysis and then make recommendations on how you should proceed based on the results.

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