Norm of Thyroid Scan
Homogeneous uptake of radioactive tracer and normal size, shape, and position of the thyroid gland.
Usage of Thyroid Scan
Differentiation of hyperfunctioning nodule and of thyroid tissue hyperplasia; help in diagnosis of thyroid cancer; evaluation of thyroid in client with history of irradiated head and neck; monitoring of the thyroid gland during therapy; used for clients with differentiated thyroid carcinoma to screen for recurrence or persistence.
Description of Thyroid Scan
A thyroid scan is a nuclear medicine scan of the thyroid after injection of a radioactive tracer (123I, 125I, 131I, or 99mTc) for the purpose of detecting areas of increased or decreased tracer uptake by the thyroid gland and surrounding area tissue. Hyperfunctioning thyroid nodules, which are usually nonmalignant, cause areas of increased uptake, labeled as “hot nodules.” “Cold nodules” are nodules that do not take up the tracer (that is, tissue is not functioning as normal thyroid tissue) and are more likely to be malignant. For detection of metastatic thyroid cancer, whole-body scanning with 131I in conjunction with levothyroxine withdrawal or stimulation with recombinant human TSH is done.
Professional Considerations of Thyroid Scan
Consent form NOT required.
Allergic reaction to tracer (itching, hives, rash, tight feeling in the throat, shortness of breath, anaphylaxis).
Previous allergy to iodine, shellfish, or radioactive tracer; pregnancy (because of the radioactive iodine crossing the blood-placental barrier); breast-feeding.
- See Client and Family Teaching.
- Have emergency equipment readily available.
- Jewelry and metal objects near the head or neck area should be removed before scanning.
- Oral radioactive tracer is administered 6 hours before scanning. Intravenous radioactive tracer is administered ½ hour before scanning.
- The client is positioned supine, with a pillow, rolled towel, or sponge beneath the shoulder blades, and the neck hyperextended.
- The thyroid gland is scanned with a gamma camera that moves over one or more sections of the thyroid gland.
- Scan takes ½ hour.
- Resume previous diet 2 hours after oral radioactive tracer administration.
- Observe the client carefully for up to 60 minutes after the study for a possible (anaphylactic) reaction to the radionuclide.
- Rubber gloves should be worn by health care providers when discarding urine for 24 hours after the procedure. Wash the gloved hands with soap and water before removing the gloves. Wash the ungloved hands after the gloves are removed. An incontinent client requires special handling of any soiled linen or disposable pads. These should be placed in special storage for a few weeks before cleaning or discarding. Consult with your radiation safety officer for details.
Client and Family Teaching
- Drugs that may be discontinued up to 21 days before the scan include anticoagulants, antihistamines, corticosteroids, cough syrup, radiopaque dyes (28–42 days), phenothiazines, salicylates, thyroxine (10 days), triiodothyronine (3 days), iodides, vitamins, and antithyroid medications such as propylthiouracil or methimazole (Tapazole) (3 days).
- Foods that should not be ingested for 14–21 days before the test include shellfish and salt or salt substitutes containing iodine.
- Fast from food and fluids for 4 hours before and 1 hour after the test if radioactive tracer will be administered orally.
- There is no discomfort with this test.
- Describe the procedure and expected sensations.
- Meticulously wash your hands with soap and water after each void for 24 hours. The toilet should be flushed 2–3 times after each voiding.
Factors That Affect Results
- If a radioactive iodine tracer is used, uptake may be increased in clients on a diet with subnormal iodine levels or those on phenothiazine therapy.
- Ingestion of drugs listed under Client and Family Teaching within 2–3 weeks before the test may cause decreased tracer uptake.
- Gastroenteritis may interfere with the absorption of orally administered radioactive tracer.
- Receipt by the client of intrathecal or intravenous contrast material within 21 days before the scan invalidates the results.
- Health care professionals working in a nuclear medicine area must follow federal standards set by the Nuclear Regulatory Commission. These standards include precautions for handling the radioactive material and monitoring of potential radiation exposure.
- Technetium half-life is 6 hours. Iodine-131 half-life is 8 days. Iodine-123 half-life is 13.3 hours.