Sequential changes in serum thyroid peroxidase following radioiodine therapy of patients with differentiated thyroid carcinoma.

To determine the detectability and the time course of serum thyroid peroxidase (TPO) levels before and 1, 2, 4, and 6 months after 131I administration, we evaluated TPO in 13 selected patients with differentiated thyroid carcinoma (DTC) whose sera did not contain antimicrosomal or antithyroglobulin (Tg) antibodies. All patients received 131I therapy 6 or 8 weeks after thyroid surgery for ablation of the postsurgical thyroid remnant. Serum samples were also collected from 10 normal subjects. Measurement of TPO was carried out by using a new commercially available immunoluminometric assay with a sensitivity of 30 pg/mL. Serum Tg was measured by RIA with a sensitivity of 2.6 micrograms/L before and 6 months after 131I administration. In all patients, a standard total body scan was obtained before and 6 months after 131I administration. TPO was undetectable in all sera from normal subjects. However, serum TPO became detectable in all patients with DTC during the study, whereas rescans were either negative or ...