The Harvard Medical School Family Health Guide
Diagnostic Tests - Thyroid Scan
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How long is it before the result of the test is known?

  • For the thyroid scan, it takes an hour or more for the pictures to be developed and additional time for a radiologist to examine them. Your doctor will probably receive a report within a day or two. The scan will show the outline, shape, and position of your thyroid so that the doctor can determine whether it is enlarged and whether there are any suspicious growths or nodules. The scan also provides a rough measure of thyroid activity, although this has to be confirmed with a radioactive iodine uptake test.
  • Uptake test results are available immediately, but because the initial and follow-up readings must be compared, it may take your doctor a day or two to get back to you. To obtain results, your doctor determines an uptake value, which is the net result of how much iodine is picked up by the thyroid, how much is converted to hormone since the time of administration, and how much is either leaked or secreted into the bloodstream. (The thyroid normally secretes hormone in an orderly fashion based on physical needs; leakage is less controlled and indicates that the gland is damaged.) A low reading of radioactivity suggests that your thyroid gland has retained only a small amount of iodine. This generally indicates that the thyroid gland is not producing excess thyroid hormone, but has become inflamed and is unable to properly store the hormone, which then leaks into the bloodstream. A high reading suggests that your thyroid is overactive, producing an excessive amount of thyroid hormone.

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