Background: Hypothyroidism is one of the most commonly treated endocrine disorders in dogs; however, the diagnosis of this condition can be challenging, potentially leading to misdiagnosis. The clinical signs of hypothyroidism are vague and non‐specific, as are the routine haematological and biochemical changes. When assessing the thyroid axis, the classical finding of decreased total thyroxine and increased thyroid‐stimulating hormone is highly specific for the diagnosis of hypothyroidism, but has less good sensitivity. Although numerous other tests are available, a basic understanding of thyroid gland physiology and thyroid test methodology is needed to be able to use each test and interpret the results correctly.
Aim of the article: This article discusses how to confidently diagnose the condition, explaining how clinicians need to consider the clinical signs, routine clinicopathological changes and thyroid hormone concentrations together, rather than in isolation.