Radioactive iodine uptake

The test is done in this way: You are given a pill that contains a tiny amount of radioactive iodine. After swallowing it, you wait as the iodine collects in the thyroid. The first uptake is usually done 4 to 6 hours after you take the iodine pill. Another uptake is usually done 24 hours later. During the uptake, you…

Follow instructions about not eating before the test. You may be told not to eat after midnight the night before your test. Your health care provider will tell you if you need to stop taking medicines before the test that may affect your test results. Do not stop taking any medicine without first talking to your…

There is no discomfort. You can eat beginning about 1 to 2 hours after swallowing the radioactive iodine. You can go back to a normal diet after the test.

This test is done to check thyroid function. It is often done when blood tests of thyroid function show that you may have an overactive thyroid gland .

These are normal results at 6 and 24 hours after swallowing the radioactive iodine: At 6 hours: 5% to 15% At 24 hours: 10% to 30% Some testing centers measure only at 24 hours. Values may vary depending on the amount of iodine in your diet. Normal value ranges may vary slightly among different labs. Talk to your…

Higher-than-normal uptake may be due to an overactive thyroid gland. The most common cause is Graves disease . Other conditions can cause some areas of higher-than-normal uptake in the thyroid gland. These include: An enlarged thyroid gland that contains nodules producing too much thyroid hormone ( toxic nodular…

All radiation has possible side effects. The amount of radiation in this test is very small, and there have been no documented side effects. Women who are pregnant or breastfeeding should not have this test. Talk to your provider if you have concerns about this test.

The radioactive iodine leaves your body through your urine. You need not take special precautions, such as flushing twice after urinating, for 24 to 48 hours after the test because the dose of radioactive iodine is very low. Ask your provider or the radiology/nuclear medicine team performing the scan about taking…

Faix JD. Thyroid function testing (thyrotropin, triiodothyronine, and thyroxine). In: Robertson RP, ed. DeGroot's Endocrinology . 8th ed. Philadelphia, PA: Elsevier; 2023:chap 68. Guber HA, Oprea M, Rusell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management…