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Thyroid Hormone Testing in Dogs

Thyroid Hormone Testing in Dogs

Accurate diagnosis of thyroid diseases in dogs depends on reliable testing methods. In this article, our veterinary experts in Santa Rosa will explain the importance of thyroid testing and provide an overview of test types.

What is the thyroid gland?

Situated near the trachea, the thyroid gland plays a crucial role in the production of thyroxine (T4), a vital thyroid hormone. These hormones have a wide-ranging impact on the body as they regulate the metabolic rate. Working in conjunction with the thyroid gland, the pituitary gland, located at the base of the brain, oversees thyroid function through the secretion of thyroid stimulating hormone (TSH).

What is thyroid testing?

A thyroid test is a blood test specifically designed to assess the functionality of the thyroid gland. It is a recommended diagnostic tool for evaluating the health of any sick animal and is commonly employed as a screening test to identify underlying illnesses or diseases. Normal test results contribute to the determination of overall health and help rule out certain conditions.

In cases where the animal is prone to excessive bleeding, extra precautions should be taken after collecting the blood sample to prevent any hemorrhaging from the site of sample extraction. Careful handling and appropriate measures are implemented to ensure the well-being of the animal during and after the testing process.

How thyroid testing is done in dogs

Before any tests are done, make sure to book a pet examination to determine if this is the proper course of action. To conduct a thyroid test, a blood sample is obtained by drawing blood from the animal. The collected blood is then placed in a specialized glass tube and separated into two components: serum and blood clot. The serum, which contains the necessary components for testing, is extracted and sent to a laboratory for analysis, while the blood clot is discarded. While certain veterinary hospitals may have the capability to perform thyroid tests in-house, many rely on external laboratories for this procedure.

When performed at the veterinary hospital, a thyroid test typically takes approximately 40-60 minutes to complete. However, if the sample is sent to an outside laboratory, the results can be expected within 1-2 days.

In most cases, dogs do not require sedation or anesthesia for the procedure. However, there are instances where dogs may exhibit aversion to needles and may need anesthesia to ensure a smooth and stress-free experience. This ensures the safety and comfort of the dog during the blood draw process.

What are some common types of thyroid tests?

The following are some of the most common thyroid tests done 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 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

To differentiate true hypothyroidism from euthyroid sick conditions, a reliable assay for measuring free T4 (FT4) is employed. FT4 refers to the non-protein bound form of thyroxine found in the bloodstream. It is present in lower concentrations compared to total T4. To accurately measure FT4, a method that effectively separates the protein-bound hormone from the free (unbound) hormone is necessary.

The Equilibrium Dialysis (ED) method is considered the gold standard test for dogs. This procedure involves an overnight incubation in a buffer and dialysis cells to separate the bound T4 from the free T4. On the other hand, the Immulite method is a faster and more cost-effective alternative to ED, providing results that are comparable to those obtained through dialysis. Monitoring thyroid supplementation using FT4 is particularly important in dogs known or suspected to have thyroid autoantibodies, as these tests help eliminate the effects of autoantibodies.

By utilizing valid FT4 testing methods like ED or Immulite, veterinarians can accurately assess thyroid function and determine appropriate treatment approaches for dogs with thyroid-related conditions.

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

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.

If you suspect your dog is suffering from a thyroid issue, contact our Santa Rosa vets to schedule an appointment. 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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