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 one week before the study. Examples of restricted items include iodized salt, prepared or processed foods high in iodized salt, seaweed, kelp, shellfish; thyroid or anti-thyroid medications; vitamins and dietary supplements. 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 iodine not used is excreted in the urine. The thyroid gland does not distinguish between radioactive and nonradioactive iodine. 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.

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. Explain to the female patient that she will be asked the date of her last menstrual period and pregnancy testing may be performed to determine the possibility of pregnancy before she is exposed to radiation.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be moments of discomfort or pain experienced if an IV line is inserted to allow infusion of fluids such as saline, anesthetics, sedatives, radionuclides, medications used in the procedure, or emergency medications.
  • Explain that an I-123 will be administrated orally (pill form).
  • Explain that the procedure is performed in a nuclear medicine department by a health-care provider (HCP) who specializes in this procedure, with support staff, and takes approximately 15 to 30 min.
  • Explain that the radionuclide poses no radioactive hazard and rarely produces adverse effects.
  • Advise that delayed images may be needed 2 to 24 hr later and that the patient may leave the department and return later to undergo delayed imaging.
  • 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.
  • Explain that once the study is completed, the needle or catheter is removed and a pressure dressing applied over the puncture site.

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

  • Establishing an IV site and injection of radionuclides are invasive procedures. Complications are rare but include risk for allergic reaction (related to contrast reaction), hematoma (related to blood leakage into the tissue following needle insertion), bleeding from the puncture site (related to a bleeding disorder or the effects of natural products and medications with known anticoagulant, antiplatelet, or thrombolytic properties), or infection (which might occur if bacteria from the skin surface is introduced at the puncture site). Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, bronchospasm). Immediately report symptoms such as fast heart rate, difficulty breathing, skin rash, itching, or chest pain to the appropriate HCP. Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.

Treatment Considerations

  • Explain that the radionuclide is eliminated from the body within 6 to 24 hr. Advise the patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body, unless contraindicated.
  • Instruct the patient to resume usual diet, as directed by the HCP.
  • Provide instruction in the care and assessment of the site.
  • Explain that application of cold compresses to the puncture site may reduce discomfort or edema.

Safety Considerations

  • The patient who is breastfeeding should consult with the requesting HCP regarding alternate testing that does not involve radiation. In general, if a woman who is breastfeeding must have a nuclear scan, she should not breastfeed the infant for 72 hr after the scan, until the radionuclide has been eliminated. She should be instructed to express the milk in order to prevent cessation of milk production; the milk can be stored and used after the 3-day period.

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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