Which thyroid hormones should be tested in dogs? - briefly
In dogs, the primary thyroid hormone that should be tested is thyroxine (T4). Additionally, testing for free thyroxine (fT4) can provide a more accurate assessment of thyroid function.
Which thyroid hormones should be tested in dogs? - in detail
When evaluating thyroid function in dogs, it is essential to assess both primary and secondary messengers of the thyroid gland. The two main thyroid hormones that should be tested are total thyroxine (T4) and free thyroxine (fT4). Additionally, testing for canine thyroid-stimulating hormone (cTSH) can provide valuable insights into the functioning of the hypothalamic-pituitary-thyroid axis.
Total Thyroxine (T4): Total T4 is a primary messenger hormone produced by the thyroid gland and reflects the overall function of this gland. Measuring total T4 provides a general overview of thyroid activity. However, it is important to note that total T4 levels can be influenced by various factors such as protein binding or changes in thyroxine-binding globulin (TBG) concentration, which can lead to misinterpretation of the results.
Free Thyroxine (fT4): Free T4 represents the unbound, biologically active form of thyroxine. Measuring fT4 offers a more accurate reflection of the thyroid hormone's bioavailability and activity within the body. This test is particularly useful in cases where total T4 levels may be affected by changes in protein binding or other confounding factors.
Canine Thyroid-Stimulating Hormone (cTSH): cTSH is a secondary messenger produced by the pituitary gland, which stimulates the thyroid gland to produce thyroxine. Measuring cTSH levels provides information about the regulatory function of the hypothalamic-pituitary axis on thyroid activity. Elevated cTSH levels typically indicate hypothyroidism, while low cTSH levels may suggest hyperthyroidism or pituitary dysfunction.
In summary, a comprehensive evaluation of thyroid function in dogs should include measurements of total T4, free T4, and cTSH. These tests collectively provide a detailed picture of thyroid hormone production, bioavailability, and the regulatory feedback mechanisms within the body, enabling accurate diagnosis and management of thyroid disorders in canine patients.