Both total thyroidectomy and subtotal thyroidectomy leave a portion of normal thyroid tissue to varying degrees. Normal thyroid follicles are more capable of uptake of iodine 131 than differentiated thyroid cancer cells, and therefore cervical and distal metastases, especially smaller or diffuse metastases, are generally not easily visualized with check doses of iodine 131. Iodine nail scavenger therapy not only removes these thyroid tissues along with the included superficial carcinoma lesions and early metastases, but also allows for a definitive diagnosis of the presence of iodine-intake metastases outside of the residual thyroid tissue and allows for further treatment. In more than half of the patients, a single high dose of iodine 131 is sufficient to remove all residual thyroid tissue. Other patients may require two to three repeat treatments. Even if no thyroid cancer metastases are found to exist after iodine 131 nail clearance treatment, permanent replacement therapy with appropriate amounts of thyroid hormone is currently the most effective way to prevent thyroid cancer recurrence and metastasis.