If there is any chance that you are pregnant, or if you are breast-feeding, let your doctor know: radionuclides could harm a developing fetus or your nursing baby. Your doctor has other ways of diagnosing the problem, such as ordering additional blood tests or a thyroid ultrasound.
For about a week before a thyroid scan, your doctor may ask you to avoid certain foods and medicines that can interfere with the results, including thyroid hormones and shellfish (which contain iodine). You should inform your doctor of any vitamins or herbal supplements you are taking. You might have to fast entirely for several hours beforehand if you'll be given a radioactive iodine pill for the test. You might also need to have blood tests that check thyroid function.
You'll be asked to sign a consent form before having the test done, indicating that you understand the risks of the test and agree to have it done. As with x-rays, metal can interfere with the imaging during a thyroid scan, so you'll need to remove all jewelry and dentures.