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Thyroid Testing for Dogs

Your dog's bodily functions are regulated by hormones secreted by glands throughout their body. When these glands don't work properly, illnesses can occur. Today, our Thornton vets discuss thyroid hormones, what they do, and the purpose of thyroid testing for your dog's health.

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 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).

What is a thyroid test used for in dogs?

A thyroid test is a blood test that evaluates the thyroid gland's function. It can be used to determine if there is a normal level or low level of thyroid hormone in dogs. This is recommended any time a pet is sick and is frequently used as a screening test for underlying illness or disease. Normal results aid in determining health and excluding certain diseases.

If your dog is prone to bleeding the vet will take extra care to ensure that no hemorrhaging occurs at the sample site.

How are thyroid tests performed on 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. While certain animal hospitals have diagnostic capabilities for interpreting the data on-site, many rely on sending the sample to a lab.

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. There may be some instances, such as where the dog reacts poorly to needles, where sedation may be required.

Are there different types of thyroid tests offered?

Here are some of the most common types of thyroid hormone testing performed on dogs:

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 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 gold standard test for dogs, known for being more accurate. This type of testing 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, 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 that can indicate whether there is likely immune-mediated (lymphocytic) thyroiditis. This test is used in conjunction with others when diagnosing thyroid-related conditions and illnesses 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.

If you would like to learn more about low thyroid in dogs and how dogs with low thyroid levels can be treated, contact our Thornton vets.

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