Which test is commonly used to confirm a diagnosis of Hashimoto's thyroiditis?

To confirm a diagnosis of Hashimoto's thyroiditis, the most specific and commonly used test is the antimicrosomal antibody test, also referred to as the thyroid peroxidase antibody test (TPOAb). This test assesses the presence of antibodies against thyroid peroxidase, an enzyme critical for thyroid hormone production. The presence of these antibodies is highly indicative of autoimmune thyroid conditions, particularly Hashimoto’s thyroiditis.

While serum TSH (Thyroid Stimulating Hormone) and free T4 tests are important for evaluating thyroid function and may help in assessing the extent of thyroid dysfunction that can occur in Hashimoto's, they do not specifically confirm the diagnosis of the condition itself. Elevated TSH and low free T4 can indicate hypothyroidism, which may occur in Hashimoto's thyroiditis, but they do not provide direct evidence of the autoimmune process.

In summary, while TSH and free T4 tests are relevant in the overall assessment of thyroid status, the antimicrosomal antibody test is the definitive assay for diagnosing Hashimoto's thyroiditis, making it the most appropriate choice to confirm the condition.