What do I have to do before my thyroid scan?

If hyperthyroidism. If you are having a diagnostic dose of i-123 (usually 200 microci), you should stop taking anti-thyroid medications (methimazole and ptu) and make sure you didn't have iodine-based IV contrast (used in ct scans) in the prior 6-8 weeks. For a diagnostic study a low-iodine diet is not require, unless you are going to received i-131 treatment shortly after the test.
Prep 4 thyroid scan. It's depends on why the scan is done but here is a good link on what you need to know: http://www.Webmd.Com/a-to-z-guides/thyroid-scan.
Supply information. Let them know had CT scan, surgeries or treatments using iodinated contrast material within the last two months, taking medications or ingesting other substances that contain iodine, including kelp, seaweed, cough syrups, multivitamins,heart medications. any allergies to iodine, medications and anesthetics.pregnant or breastfeeding.Isotope used either Iodine 123 ingested or Technetium 99m IV.
Avoid iodized salt, Anything containing iodine competes for uptake into the thyroid. Sushi bar seaweed or iodized salt decrease isotope in the thyroid.