In canine hypothyroidism testing, which statement is true?

• A. TSH stimulation tests are mandatory for all cases
• B. Thyroglobulin antibody tests are diagnostic on their own
• C. TSH stimulation tests are rarely needed; antibodies may support autoimmune thyroiditis but are not routinely diagnostic
• D. Any hypothyroidism case can be diagnosed with a single T4 measurement

Answer: (C)

In diagnosing canine hypothyroidism, no single test confirms the disease for every dog. A low T4 can occur with non-thyroidal illness, medications, or assay issues, so clinicians look at the bigger picture: clinical signs plus additional thyroid tests and context. The TSH stimulation test used to be more commonly described as a gold standard, but it is rarely needed now because it’s invasive, costly, and many dogs with hypothyroidism don’t show a consistent T4 response. So in most cases, you don’t routinely rely on a TSH stimulation test to make the diagnosis.

Sometimes antibodies against thyroid components, like thyroglobulin antibodies, are checked because their presence can support an autoimmune thyroiditis process. However, these antibodies are not diagnostic on their own—some hypothyroid dogs may not have detectable antibodies, and antibodies can be found in dogs without clinical disease. So antibody testing may help but is not definitive for diagnosing hypothyroidism.

Dismissing any single T4 measurement as diagnostic is not appropriate because of the potential for false positives or negatives due to illness or drugs; and insisting on a TSH stimulation test for all cases is not consistent with current practice.