What diagnostic test is used to assess the presence of antibodies against thyroid peroxidase?

The diagnostic test used to assess the presence of antibodies against thyroid peroxidase is the TPO antibody test. This test specifically measures the level of antibodies that target thyroid peroxidase, an enzyme crucial for the synthesis of thyroid hormones. Elevated levels of these antibodies are often associated with autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease, indicating an immune response against the thyroid gland.

In contrast, a thyroid panel generally includes measurements of thyroid hormones (like TSH, T3, and T4) and may also test for thyroglobulin antibodies, but it does not specifically measure TPO antibodies. Radioactive iodine uptake assesses how well the thyroid gland is functioning and helps evaluate conditions such as hyperthyroidism, but does not involve antibody testing. Fine needle aspiration biopsy is performed to obtain tissue samples for cytological examination, particularly in the context of thyroid nodules, but again, it does not provide information about the presence of antibodies against thyroid peroxidase.

Thus, the TPO antibody test is the definitive method for determining the presence of these antibodies, making it the correct answer.