Radioactive Iodine Uptake

General

Synonym/Acronym:

RAIU, thyroid uptake.

Rationale

To assess thyroid function toward diagnosing disorders such as hyperthyroidism and goiter.

Patient Preparation

There are no activity restrictions unless by medical direction. Instruct the patient to fast and restrict fluids for 8 to 12 hr before the procedure. The patient may be instructed, by medical direction, to restrict foods, medicines, or supplements containing iodine for 1 to 2 wk before the study. Examples of restricted items include dairy products, whole eggs or egg yolk, iodized salt, prepared or processed foods high in iodized salt, seaweed, kelp, shellfish; thyroid or antithyroid medications; vitamins and dietary supplements; foods or medications with red dye #3. The thyroid gland does not distinguish between radiolabeled and natural iodine; restricting dietary intake helps ensure optimal uptake of radiolabeled iodine for accurate study results. The patient may eat 4 hr after the injection unless otherwise indicated. Protocols may vary among facilities.

Normal Findings

  • Variations in normal ranges of iodine uptake can occur with differences in dietary intake, geographic location, and protocols among laboratories:
Iodine UptakePercentage of Radionuclide
6-hr absorption2%–16%
24-hr absorption8%–25%

Critical Findings and Potential Interventions

N/A

Overview

(Study type: Nuclear scan; related body system: Endocrine system.)

Radioactive iodine uptake (RAIU) is a nuclear medicine study used for evaluating thyroid function. It directly measures the ability of the thyroid gland to concentrate and retain circulating iodide for the synthesis of thyroid hormone. RAIU assists in the diagnosis of both hyperthyroidism and hypothyroidism, but it is more useful in the diagnosis of hyperthyroidism.

A very small dose of radioactive iodine is administered orally in a capsule or liquid, and radioactivity counts are taken with a gamma probe at specified intervals after the initial dose is administered. The most commonly used isotopes are iodine-123 (I-123) or I-131. I-123 tends to be used more frequently because I-131 has a much longer half-life and therefore a longer period of radiation exposure. The radionuclide emits gamma radiation, which allows external measurement. The uptake of radionuclide in the thyroid gland is measured as the percentage of radionuclide absorbed in a specific amount of time. The thyroid gland does not distinguish between radioactive and nonradioactive iodine. The iodine not used is excreted in the urine. Uptake values are used in conjunction with measurements of circulating thyroid hormone levels to differentiate primary and secondary thyroid disease, and serial measurements are helpful in long-term management of thyroid disease and its treatment. I-131 may also be used therapeutically, in much stronger doses than used in the RAIU scan, to treat thyroid cancer.

Indications

  • Evaluate hyperthyroidism and/or hypothyroidism.
  • Evaluate neck pain.
  • Evaluate the patient as part of a complete thyroid evaluation for symptomatic patients (e.g., swollen neck, neck pain, extreme sensitivity to heat or cold, jitters, sluggishness).
  • Evaluate thyroiditis, goiter, or pituitary failure.
  • Monitor response to therapy for thyroid disease.

Interfering Factors

Contraindications

Pregnancy is a general contraindication to procedures involving radiation.

Factors that may alter the results of the study

  • Recent use of iodinated contrast medium for radiographic studies (within the last 4 wk) or nuclear medicine procedures done within the previous 24 to 48 hr.
  • Iodine deficiency (e.g., patients with inadequate dietary intake, patients on phenothiazine therapy), which can increase radionuclide uptake.
  • Certain drugs and other external sources of excess iodine, which can decrease radionuclide uptake, as follows:
    • Foods containing iodine (e.g., iodized salt, shellfish)
    • Drugs and other substances such as aminosalicylic acid, antihistamines, antithyroid medications (e.g., propylthiouracil), corticosteroids, cough syrup, isoniazid, levothyroxine sodium/T4, l-triiodothyronine, Lugol solution, nitrates, penicillins, potassium iodide, propylthiouracil, saturated solution of potassium iodide, sulfonamides, thyroid extract, tolbutamide, warfarin
    • Multivitamins containing minerals
  • Vomiting, severe diarrhea, and gastroenteritis, which can affect absorption of the oral radionuclide dose.

Potential Medical Diagnosis: Clinical Significance of Results

Abnormal Findings In:

  • Decreased iodine intake or increased iodine excretion
  • Graves disease
  • Iodine-deficient goiter
  • Hashimoto thyroiditis (early)
  • Hyperthyroidism, increased uptake of radionuclide:
    • Rebound thyroid hormone withdrawal
    • Drugs and hormones such as barbiturates, diuretics, estrogens, lithium carbonate, phenothiazines, and thyroid-stimulating hormone
  • Hypothyroidism, decreased uptake of 0% to 10% radionuclide over 24-hr period:
    • Chronic kidney disease
    • Hypoalbuminemia
    • Malabsorption
    • Subacute thyroiditis
    • Thyrotoxicosis as a result of ectopic thyroid metastasis

Nursing Implications, Nursing Process, Clinical Judgement

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Discuss how this test can assist in assessing thyroid function.
  • Explain that the procedure takes about 15 to 30 min and is performed in a nuclear medicine department.
  • Review the procedure with the patient.
  • Explain that pregnancy testing may be required.
  • Explain that the radionuclide will be administrated orally (pill form or liquid), usually 24 hr prior to the test.
  • Reassure the patient that the radionuclide poses no radioactive hazard and rarely produces adverse effects.

Procedural Information

  • Policies regarding breastfeeding before and after an imaging procedure may vary among facilities. For additional information, see Appendix A: Patient Preparation and Specimen Collection, subsection: Potential Contraindications and Complications Associated With Diagnostic Procedures.
  • Baseline vital signs are recorded and monitored throughout the procedure.
  • Positioning for this procedure is lying in a supine position on a table; the gamma probe/detector is placed over the neck.
  • The patient is instructed to return to the nuclear medicine department at various intervals if delayed gamma probe counts are needed (usually 6 hr and 24 hr).

Potential Nursing Actions

Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

After the Study: Implementation & Evaluation Potential Nursing Actions

Avoiding Complications

  • Monitor the patient for complications related to the procedure.

Treatment Considerations

  • Follow postprocedure vital sign and assessment protocol.
  • Explain that the radionuclide is eliminated from the body within 6 to 24 hr.
  • Advise drinking increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body, unless contraindicated.
  • Resume usual diet, as directed by the health-care provider.
  • Review symptoms of hyperthyroidism as indicated; tachycardia, arrhythmia, weight loss, heat sensitivity, menstrual pattern changes, tremors, thin skin, insomnia, weakness, fatigue, frequent bowel movements, goiter, sweating, anxiety, nervousness, increased appetite.

Safety Considerations

  • Refer to organizational policy for additional precautions that may include instructions on suspension of breastfeeding, hand washing, toilet flushing, limited contact with others, and other aspects of nuclear medicine safety.

Clinical Judgement

  • Consider which educational approach would best support treatment recommendations such as surgery or medication.

Followup Evaluation and Desired Outcomes

  • Understands that depending on the results of this procedure, additional testing may be needed to evaluate or monitor disease progression and determine the need for a change in therapy.

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