Can a breastfeeding patient undergo a radioiodine (iodine-131) uptake scan for thyroid evaluation?

Radioiodine Uptake Scan During Breastfeeding

No, breastfeeding patients should not undergo radioiodine uptake scans without interrupting or permanently stopping breastfeeding, depending on which radioactive isotope is used. 1

Critical Isotope-Specific Recommendations

The management depends entirely on which radioactive iodine isotope will be administered:

For I-123 (Iodine-123) Scans

• Interrupt breastfeeding for at least 2 days after the scan 1
• Express and discard breast milk during this 2-day period 1
• Breastfeeding can be resumed after this interruption period 1
• I-123 has a shorter half-life and delivers lower radiation doses compared to I-131 1

For I-131 (Iodine-131) Scans

• Permanently discontinue breastfeeding - do not resume 1, 2
• I-131 has an 8-day half-life and delivers significantly higher radiation doses 3, 1
• Lactating mothers who receive I-131 should not breastfeed their infant from that point forward 2
• However, breastfeeding in future pregnancies (after the current lactation period has ended) is not contraindicated 2

Physiologic Rationale for These Restrictions

Radioactive iodine is actively concentrated and excreted into breast milk, creating direct radiation exposure risk to the nursing infant 1, 4:

• The infant's thyroid gland is particularly radiosensitive and iodine-avid, making exposure especially concerning 1
• Many radiopharmaceuticals, including radioiodine, are excreted through breast milk 4
• The goal is to keep the effective radiation dose to the infant below 1 mSv 4
• Radioactive iodine readily crosses into breast milk and can cause concentrated radiation damage to the infant's thyroid 5

Critical Distinction: Radioactive vs. Non-Radioactive Iodine

This recommendation applies ONLY to radioactive iodine isotopes (I-123 or I-131), not to non-radioactive iodinated CT contrast 1:

• Non-radioactive iodinated CT contrast does not require any breastfeeding interruption 3, 1
• Less than 1% of iodinated CT contrast is excreted into breast milk, and less than 1% of that is absorbed by the infant 3
• Lactating women do not need to discontinue breastfeeding after receipt of intravascular iodinated contrast 3

Pre-Scan Counseling and Planning

Before scheduling the scan, confirm which isotope will be used 1:

• This determines whether breastfeeding can eventually be resumed (I-123) or must be permanently stopped (I-131) 1
• Counsel the mother on the specific implications for breastfeeding based on the isotope 1
• If I-123 is available and clinically appropriate, it should be preferred over I-131 for diagnostic purposes in breastfeeding women 3
• I-123 is generally preferred over I-131 for diagnostic thyroid imaging due to superior imaging quality 3

Common Pitfalls to Avoid

• Do not confuse radioactive iodine with non-radioactive CT contrast - they have completely different breastfeeding recommendations 1
• Do not assume all radioiodine scans use the same isotope - I-123 and I-131 require different breastfeeding management 1
• Do not underestimate breast uptake of radioiodine - the lactating breast actively concentrates radioiodine and can show significant uptake patterns on imaging 6, 7
• Be aware that breast uptake can occur even in non-lactating women with recent breastfeeding history (mean 11.4 months after cessation) 7