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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 Clackamas vets discuss what thyroid testing is, how thyroid testing is done, and some common types of tests.

What is the thyroid gland?

Thyroxine (T4), a significant thyroid hormone, is produced by the thyroid gland, which is close to the trachea. Thyroid hormones control metabolic rate, which has a significant impact on the body. Thyroid-stimulating hormone (TSH), produced by the pituitary gland at the base of the brain, controls thyroid gland activity.

What is thyroid testing?

A thyroid test is a blood test that determines how well the thyroid gland is working. In addition to being frequently used as a screening test for underlying illness or disease, it is advised in any sick animal. Results that are normal help determine health and rule out particular 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?

The blood sample needed for a thyroid test must be drawn, divided into serum and blood clot, and then put in a special glass tube. While the blood clot is discarded, the serum is extracted and sent to a lab for analysis. While some veterinary hospitals have their own labs, the majority rely on outside testing facilities to perform thyroid exams.

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

Total T4 (Thyroxine) and Total T3 (Triiodothyronine) testing in dogs can be used to detect hypothyroidism. T3 and T4 concentrations can be influenced by a variety of factors such as 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, requiring 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 detects autoimmune thyroiditis in dogs. It should be used in conjunction with other thyroid tests for a more precise diagnosis. Autoantibodies to thyroglobulin 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.

Do you suspect your dog is suffering from a thyroid issue? Don't hesitate to contact our Clackamas 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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