The thyroid is a small, butterfly-shaped gland in your dog's throat that produces hormones to control his metabolism and growth. When the thyroid malfunctions, the dog's health goes out of whack in multiple ways. A number of illnesses mimic thyroid disease, so blood chemistry is studied in conjunction with other symptoms to determine what might be ailing your dog.
Thyroid problems occur when the gland secretes either too many or too few hormones. If it is secreting more than the body needs, the condition is called hyperthyroidism. If it isn't secreting enough, it is called hypothyroidism. Either condition is unhealthy for your dog since thyroid hormones control his metabolism. Hypothyroidism, or low levels of thyroid hormones, is more common than its opposite. Symptoms of hypothyroidism include unexplained weight gain, dry skin, lethargy, anemia and muscle weakness.
Routine Blood Work
Whether or not thyroid function is included in routine blood work depends on your veterinarian. Many include basic thyroid tests as part of an annual exam. Checking thyroid levels on an annual basis, even if your dog seems perfectly healthy, establishes a baseline level, the level that's normal for your particular dog. Your veterinarian can compare the dog's yearly results to determine whether worrisome changes have occurred. This is one of the few ways to catch problems early, since most dogs don't show symptoms of thyroid disease until the gland has been permanently damaged.
Blood tests specifically for checking the thyroid include several components. A thyroid panel checks three types of hormone levels: T3, T4 and free T4. Individually, these tests provide a small amount of information about thyroid function, but combined they paint a clearer picture of whether your dog's thyroid is secreting hormones at a healthy rate. This is because individual results have a wide range of normal values; one test showing results at the low end of the normal range may not be cause for concern. More than one test coming in at the low end, however, may be an indicator that there is a problem.
If initial blood tests reveal that your dog has thyroid problems, an additional antibody blood test can reveal whether the issue is being caused by autoimmune disease. If initial testing is inconclusive, your veterinarian may test the level of thyroid stimulating hormones in your dog's blood. This test does not always confirm hypothyroidism, but it adds another small piece to the overall picture of your dog's health. If your veterinarian suspects thyroid disease but is unable to confirm it through blood tests, he may treat your dog with medication and continue with regular blood testing to see how your dog responds.