Patients are classified as being free of disease after total or near-total thyroidectomy and 131I remnant ablation when all of the following criteria are fulfilled:
• Complete resection of identifiable tumor.
• No uptake outside the thyroid bed on the posttherapy whole body 131I scan.
• Negative neck ultrasound examination.
• Undetectable serum Tg levels (<1 mg/L) during both:
thyroid hormone suppression of TSH and TSH stimulation.
TSH stimulation of Tg can be achieved either by administering recombinant human TSH (rhTSH, Thyrogen, Figure 20.1) or by withdrawing thyroid hormone (THW) long enough, usually 2 to 3 weeks, to raise TSH levels above 30mIU/L [1,2]. This is necessary because meas
uring serum Tg concentrations during thyroid hormone suppression of TSH (THST) frequently fails to identify persistent tumor or identifies it late in its course when it is at a more advanced stage [3-6]. Likewise, performing diagnostic whole-body scans (DxWBS), whether after THW or with rhTSH administration, often fails to identify persistent tumor. On the other hand, posttreatment whole-body 131I scans (RxWBS) and neck ultrasonography are powerful tools with which tumor may be identified at an early stage [3-6].
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