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radioactive iodine uptake (RAIU) test
Indications:
- suspected thyrotoxicosis
Contraindications:
1) pregnancy
2) lactation
3) normal or elevated serum TSH [1]
4) suspected iodine-induced hyperthyroidism
Reference interval:
- I-123 uptake, normal range:
a) 3-16% in 6 hours
b) 8-25% in 24 hours
Principle:
- measures uptake of radiolabeled iodine by the thyroid gland over a period of 24 hours.
Increases:
1) increased thyroid-stimulating hormone
- primary hyperthyroidism
2) iodine deficiency
3) thyroid hyperfunction
a) autonomous nodules
- toxic multinodular goiter can show patchy, irregular uptake & areas of increased uptake [1]
b) Grave's disease
- shows diffuse uptake
- uptake may be different in the two lobes
- multiple scans may be shown without explanation
- uptake in the different scans may be quite different
Decreases:
1) factitious thyrotoxicosis
2) iodine excess (iodine-induced hyperthyroidism)
3) hypothyroidism
4) thyroiditis resulting in release of preformed thyroid hormone [1]
Related
thyroid disease
General
scintigraphy (radionuclide test)
References
- Medical Knowledge Self Assessment Program (MKSAP) 11, 15, 16,
17. American College of Physicians, Philadelphia 1998, 2009, 2012, 2015
- Medical Knowledge Self Assessment Program (MKSAP) 20
American College of Physicians, Philadelphia 2025
- NEJM Knowledge+