Radioactive Iodine Uptake

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 anti-thyroid 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. Ensure that this procedure is performed before all radiographic procedures using iodinated contrast medium.

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
2-hr absorption1%–13%
6-hr absorption2%–25%
24-hr absorption15%–45%

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-123 (I-123) or I-131 is administered orally, and images are taken at specified intervals after the initial dose is administered. 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

Patients who are pregnant or suspected of being pregnant, unless the potential benefits of a procedure using radiation far outweigh the risk of radiation exposure to the fetus and mother.

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.
  • Metallic objects (e.g., jewelry, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.
  • Inability of the patient to cooperate or remain still during the procedure, because movement can produce blurred or otherwise unclear images.

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

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Inform the patient this test can assist in assessing thyroid function.
  • Pregnancy is a general contraindication to procedures involving radiation; lower radiation emission technology allows for safe performance of many imaging procedures during pregnancy. The I-123 radionuclide has a low radioactive emission and short half life. The facility’s imaging polices should always be followed.
  • Explain to the female patient that she may be asked the date of her last menstrual period. Pregnancy testing may be performed in accordance with the facility’s imaging and radionuclide administration policies. In all cases, the benefits and risks should be discussed with the HCP before proceeding with the study.
  • Explain to the patient who is breastfeeding that the benefits and risks of breastfeeding should be discussed with the HCP before the patient makes an informed decision to continue or temporarily suspend breastfeeding. Policies may vary among facilities. Facility guidelines may recommend complete cessation of breastfeeding or suspending breastfeeding for a period of time during which the infant may be bottle fed with milk expressed prior to the procedure.
  • Review the procedure with the patient.
  • Explain that an I-123 radionuclide will be administrated orally (pill form).
  • Explain that the procedure takes about 15 to 30 min and is performed in a nuclear medicine department.
  • Discuss that delayed images may be needed 2 to 24 hr requiring a return to the nuclear medicine department.
  • Reassure the patient that the radionuclide poses no radioactive hazard and rarely produces adverse effects.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined.
  • Baseline vital signs and neurological status are recorded. Protocols may vary among facilities.
  • Positioning for this procedure is in a sitting or supine position in front of a radionuclide detector.

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: Potential Nursing Actions

Avoiding Complications

  • Monitor the patient for complications related to the procedure (e.g., ageusia [loss of taste], nausea and vomiting, pain, and swelling of the salivary glands).

Treatment Considerations

  • Explain that the radionuclide is eliminated from the body within 6 to 24 hr.
  • Unless contraindicated, advise the patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body.
  • Instruct the patient to resume usual diet, as directed by the HCP.

Safety Considerations

    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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