The thyroglobulin (Tg) test is a blood test used to measure the level of thyroglobulin in the bloodstream. Thyroglobulin is a protein produced by the thyroid gland, and it plays a crucial role in the production of thyroid hormones. The Tg test is often used to monitor patients who have had thyroid cancer and have undergone treatment, such as thyroid surgery or radioactive iodine therapy. In these cases, the Tg test is used to detect any residual thyroid tissue or cancer cells that may be present in the body. The Tg test may also be used to monitor patients with thyroid nodules or goiter, as well as those with autoimmune thyroid disorders. Overall, the Tg test is a useful tool for evaluating thyroid function and monitoring thyroid disease.