T4 Tests for Diagnosing Canine Hypothyroidism

Canine hypothyroidism is a disease of the thyroid gland, a part of your pet's body that regulates his metabolism and creates a variety of important hormones that influence his bodily functions. Hypothyroidism is a serious health condition with lasting and damaging effects, but it can be very difficult to diagnose due to a variety of symptoms that are relatively common. An increasing number of vets have turned to specific blood tests to help make an accurate diagnosis of hypothyroidism. A T4 blood test is one of the most common and reliable methods for determining whether your dog suffers from this condition.

The T4 Hormone and Hypothyroidism

T3 and T4 are names of two of the primary hormones that are produced and regulated by the thyroid gland. These chemicals serve to regulate your pet's metabolism. In the case of hypothyroidism, your pet's thyroid gland functions below its standard capacity, and these hormone levels will be affected. The result is that your pet may suffer a range of related symptoms. The most common of these symptoms include:

  • Increased appetite and weight gain
  • Dry, flaky skin
  • Redness or irritation on the skin
  • Hair loss

Hypothyroidism is most common in moderately sized dogs or larger breeds, and generally develops after 5 years of age. However, it can be present in any breed of dog and at any level of development, so it's important to be mindful if your pet displays any of the symptoms listed above.

Testing for Hypothyroidism with T4 Tests

If your veterinarian suspects that your pet may be suffering from hypothyroidism, he will begin by running a baseline T4 test. This analysis of your dog's blood serves to give a reading of the T4 level at any given time. If you haven't tested your dog's T4 level before, it can be difficult to ascertain whether his T4 level is normal or not. Still, many dogs with hypothyroidism show dramatically low T4 levels, which is a primary indication of the condition.

A baseline T4 test can be conducted easily and painlessly, and involves a simple blood sample and analysis. If your pet is diagnosed with hypothyroidism, your vet will likely conduct this test periodically in order to determine how your dog's T4 levels change over time, and in response to certain treatments.

For a more accurate reading of your pet's T4 levels, your veterinarian may perform a free T4 analysis as well. Bounded T4 is chemically attached to various proteins throughout your pet's body, while free T4 is available to move around and perform various functions. An equilibrium dialysis test is used to determine the free T4 levels in your pet's blood.

Thyroid Stimulating Hormone (or TSH) tests are also helpful in diagnosing hypothyroidism. TSH activates the thyroid and causes a spike in T4 levels in healthy dogs. By administering TSH to your pet and then sampling his blood for a T4 reading, your vet can determine if your pet's low T4 levels are based on a thyroid condition. Dogs suffering from hypothyroidism will not experience a spike in T4 levels after treatment with TSH.

Between these three tests, your veterinarian can make an accurate diagnosis of canine hypothyroidism. Following these exams, you and your vet can work together to develop an appropriate treatment plan.