What are the recommendations for a breastfeeding woman undergoing a radioactive iodine uptake scan?

Radioactive Iodine Uptake Scan and Breastfeeding

Breastfeeding should be discontinued for at least 2 days after a radioactive iodine uptake scan using I-123, and stopped completely if I-131 is used. 1

Critical Distinction: Diagnostic Scan vs. CT Contrast

The recommendations for radioactive iodine scans differ fundamentally from iodinated CT contrast:

• Radioactive iodine (I-123 or I-131) requires breastfeeding interruption due to radioactive isotope excretion into breast milk 1
• Non-radioactive iodinated CT contrast does not require any breastfeeding interruption, as less than 0.01% appears in breast milk and even less is absorbed by the infant 1, 2

Specific Recommendations by Isotope

I-123 (Iodine-123)

• Interrupt breastfeeding for at least 2 days after the scan 1
• This shorter interruption period reflects I-123's shorter half-life and lower radiation dose compared to I-131 1

I-131 (Iodine-131)

• Cease breastfeeding completely - do not resume 1
• I-131 has an 8-day half-life and delivers significantly higher radiation doses (0.14 mSv/MBq for I-131 vs. 0.013 mSv/MBq for I-123) 1
• The prolonged half-life poses sustained radiation exposure risk to the nursing infant 3

Physiologic Rationale

Radioactive iodine concentrates in breast milk because:

• The mammary gland actively transports iodine, similar to the thyroid gland 4
• Radioactive iodine readily crosses into breast milk and can be absorbed by the infant's gastrointestinal tract 4
• The infant's thyroid is particularly radiosensitive and iodine-avid, making exposure especially concerning 5

Practical Management

Before the scan:

• Confirm which isotope (I-123 vs I-131) will be used, as this determines whether breastfeeding can ever be resumed 1
• Advise the mother to pump and store breast milk in advance if I-123 is being used 4
• If I-131 is planned, counsel that permanent cessation of breastfeeding will be required 1

After I-123 administration:

• Express and discard breast milk for at least 2 days 1
• Some protocols recommend measuring breast milk radioactivity before resuming feeding to ensure safety 4, 6
• The 2-day minimum may need extension based on administered activity and individual clearance 4

After I-131 administration:

• Permanently discontinue breastfeeding 1
• Do not attempt to "pump and dump" until safe, as the 8-day half-life makes this impractical 1

Common Pitfalls

• Confusing radioactive iodine with CT iodinated contrast: CT contrast requires no breastfeeding interruption whatsoever 1, 2
• Assuming all nuclear medicine studies have the same breastfeeding recommendations: Different radiopharmaceuticals have vastly different excretion patterns and required interruption periods 4, 6
• Not verifying the specific isotope: Always confirm whether I-123 or I-131 is being used, as management differs completely 1
• Inadequate advance planning: Mothers should be counseled before the procedure about breastfeeding implications to allow milk storage or weaning decisions 4