radioactive iodine uptake (RAIU) test

Indications

• suspected thyrotoxicosis

Contraindications

• pregnancy
• lactation
• normal or elevated serum TSH
• suspected iodine-induced hyperthyroidism

Reference interval

• I-123 uptake, normal range:
  • 3-16% in 6 hours
  • 8-25% in 24 hours

Principle

• measures uptake of radiolabeled iodine by the thyroid gland over a period of 24 hours.

Increases

• increased thyroid-stimulating hormone
  • primary hyperthyroidism
• iodine deficiency
• thyroid hyperfunction
  • autonomous nodules
  • Grave's disease

Decreases

• factitious thyrotoxicosis
• iodine excess (iodine-induced hyperthyroidism)
• hypothyroidism
• thyroiditis resulting in release of preformed thyroid hormone

More general terms

• scintigraphy (radionuclide test)

Additional terms

• thyroid disease