Thyroglobulin (Tg) levels are monitored through blood tests. A high level of Tg may indicate metastasis (spreading of the the cancer cells), while a low level is considered to indicate the absence of cancer cells. According to the American Academy of Clinical Endocrinologists (AACE), this test is accurate 90% of the time in patients receiving higher doses of thyroid hormone to suppress the release of TSH from the pituatary gland. Some physicians feel that it is more accurate to test Tg when you are hypothyroid.
The other common follow up study is the whole body scan with I131. This is similar to the scans done for initial diagnosis. It is recommended by the AACE that the scan be done within 6-8 weeks of surgery to remove the thyroid or 3-6 months following treatment with radioiodine to ablate (destroy) the thyroid tissue. Once a negative scan is obtained, it may only be repeated if Tg levels or symptoms indicate that there may be a need. The problem is that until just recently it has been necessary to stop all thyroid hormone replacement and eat a low iodine diet for up to 6 weeks before the test to obtain accurate results.
"Going hypo," as it is referred to on the Thyroid Cancer Survivors website, means that you will experience symptoms of hypothyroidism. These can include depression, fatigue, decreased mental function, and anxiety--all difficult to cope with. Many doctors prescribe a T3 only replacement called Cytomel for the first 3 weeks, then have you stop altogether for 3 weeks. Perhaps one of the most welcomed breakthroughs for thyroid cancer survivors has been the approval of recombinant TSH (marketed as Thyrogen) for use prior to RAI scans. This drug produces the same effect as going off thyroid replacement hormone. If test results are abnormal following the injection of recombinant TSH, your doctor may want to retest following the same hypothyroid routine as before.
What if the tests are positive and the cancer is still there or has reappeared? Many people do require more than one course of radioiodine therapy or external radiation. If there is a nodule that the doctor can feel in the neck or lymph nodes, he/she may suggest further surgery. If the disease is discovered through an I131 scan, that is generally an indication that it will respond to further RAI therapy.
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