radioactive iodine uptake


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uptake

 [up´tāk]
absorption and incorporation of a substance by living tissue.
biologic uptake movement of hazardous substances from the environment into the tissues of plants or animals.
radioactive iodine uptake (radioiodine uptake) uptake of radioiodine from the blood by the thyroid gland; see radioiodine uptake test.
T3 resin uptake (triiodothyronine resin uptake) the uptake of radioactive triiodothyronine at binding sites on resin, contrasted to uptake at sites on thyroxine-binding globulin in the triiodothyronine resin uptake test.

radioactive iodine uptake (RAIU)

the absorption and incorporation by the thyroid of radioactive iodine (RAI), administered orally as a tracer dose in a test of thyroid function and as larger doses for the treatment of hyperthyroidism. The radioisotope 131I is rapidly absorbed in the stomach and concentrated in the thyroid. Normal findings are 4% to 12% absorbed in 2 hours, 6% to 15% absorbed in 6 hours, and 8% to 30% absorbed in 24 hours. Patients receiving a large therapeutic dose of RAI may require hospitalization for several days. See also radioactive iodine excretion test.

radioactive iodine uptake

RAIU, thyroid scan, thyroid scintigraphy Nuclear medicine A method of assessing thyroid function, using radioactive iodine–eg, 131I or 123I; ↑ in hyperthyroidism, ectopic hormone production, iodine deficiency, and in response to thyroid hormone depletion; ↓ in hypothyroidism, after administration of exogenous thyroid hormone, in defects of hormone storage, after exposure to iodine overload Normal range 5-25%. See T3, T4, TSH.

Radioactive Iodine Uptake

Synonym/acronym: RAIU, thyroid uptake.

Common use

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

Area of application

Thyroid.

Contrast

Oral radioactive iodine.

Description

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.

This procedure is contraindicated for

  • high alertPatients 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.

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

Potential diagnosis

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%

Abnormal findings related to

  • Decreased iodine intake or increased iodine excretion
  • Graves’ disease
  • Iodine-deficient goiter
  • Hashimoto’s 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:
    • Hypoalbuminemia
    • Malabsorption
    • Renal failure
    • Subacute thyroiditis
    • Thyrotoxicosis as a result of ectopic thyroid metastasis

Critical findings

    N/A

Interfering factors

  • Factors that may impair clear imaging

    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • 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)
      • Drugs such as aminosalicylic acid, antihistamines, antithyroid medications (e.g., propylthiouracil, iodothiouracil), corticosteroids, cough syrup, isoniazid, levothyroxine sodium/T4, l-triiodothyronine, Lugol’s solution, nitrates, penicillins, potassium iodide, propylthiouracil, saturated solution of potassium iodide, sulfonamides, thiocyanate, 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.
  • Other considerations

    • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.
    • Consultation with a health-care provider (HCP) should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating. Pediatric Considerations Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (www.pedrad.org/associations/5364/ig/).
    • Risks associated with radiation overexposure can result from frequent x-ray or radionuclide procedures. Personnel working in the examination area should wear badges to record their level of radiation exposure.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in assessing thyroid function.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, sedatives, or radionuclides.
  • Obtain a history of the patient’s endocrine system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results, including examinations using iodine-based contrast medium.
  • Ensure that this procedure is performed before all radiographic procedures using iodinated contrast medium.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Address concerns about pain related to the procedure and explain that some pain may be experienced during the test, and there may be moments of discomfort. Inform the patient that the procedure is performed in a nuclear medicine department by an HCP who specializes in this procedure, with support staff, and takes approximately 15 to 30 min. Delayed images or data collection is needed 24 hr later.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined.
  • Instruct the patient to fast and restrict fluids for 8 to 12 hr before the procedure. The patient may eat 4 hr after the injection unless otherwise indicated. Protocols may vary among facilities.

Intratest

  • Potential complications:
  • Although it is rare, there is the possibility of allergic reaction to the radionuclide. Have emergency equipment and medications readily available. If the patient has a history of allergic reactions to any substance or drug, administer ordered prophylactic steroids or antihistamines before the procedure.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure the patient has complied with dietary, fluid, and medication restrictions for 8 to 12 hr before the procedure.
  • Ensure that the patient has removed all external metallic objects from the area to be examined prior to the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Administer the I-123 orally (pill form).
  • Place the patient in a sitting or supine position in front of a radionuclide detector at 2, 6, and 24 hr after ingestion for uptake images.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual diet, as directed by the HCP.
  • Advise patient to drink increased amounts of fluids for 24 hr to eliminate the radionuclide from the body, unless contraindicated. Tell the patient that radionuclide is eliminated from the body within 24 to 48 hr.
  • If a woman who is breastfeeding must have a nuclear scan, she should not breastfeed the infant until the radionuclide has been eliminated. This could take as long as 3 days. She should be instructed to express the milk and discard it during the 3-day period to prevent cessation of milk production.
  • Instruct the patient to immediately flush the toilet and to meticulously wash hands with soap and water after each voiding for 24 hr after the procedure.
  • Instruct all caregivers to wear gloves when discarding urine for 24 hr after the procedure. Wash gloved hands with soap and water before removing gloves. Then wash hands after the gloves are removed.
  • Recognize anxiety related to test results, and be supportive of perceived loss of independent function. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ACTH, albumin, ACE, antibodies antithyroglobulin, biopsy thyroid, BUN, CT spine, copper, creatinine, cystoscopy, fecal analysis, fecal fat, FSH, gastric emptying scan, GH, LH, PTH, protein, thyroglobulin, thyroid binding inhibitory immunoglobulins, thyroid scan, TSH, TSI, thyroxine, free T4, triiodothyronine, free T3, US thyroid, upper GI series, and UA.
  • Refer to the Endocrine System table at the end of the book for tests by related body system.
References in periodicals archive ?
Linear regression analysis, after adjusting for age, gender, free thyroid hormone levels, thyroid autoantibodies, thyroid volume, and radioactive iodine uptake, showed that thyroid volume is the sole independent variable associated with nodule diameter (beta=0.
As with a radioactive iodine uptake test described earlier, in a thyroid scan you swallow a radioactive chemical (usually iodine or technetium).
Several studies have been conducted to determine the relative effects of perchlorate, thiocyanate, and nitrate on radioactive iodine uptake (RAIU) inhibition.

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