Medical Specialty >> Endocrinology

Doctors Lounge - Endocrinology Answers

Back to Endocrinology Answers List

If you think you may have a medical emergency, call your doctor or 911 immediately. Doctors Lounge ( does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on the Site.

DISCLAIMER: The information provided on is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her physician. Please read our 'Terms and Conditions of Use' carefully before using this site.

Date of last update: 10/17/2017.

Forum Name: Endocrinology Topics

Question: why would I take r-123 instead of r-131 for a thyroid scan w

 allylang1 - Mon Apr 13, 2009 2:59 pm

I have a thyroid scan with uptake tomorrow but was wondering why they gave me r-123 instead of r-131 like a friend of mine had? Thank you
 Dr. N. Haider - Thu Apr 23, 2009 4:27 pm

User avatar hi allylang1
How did the scan go? When do you expect the results to be back?
I think it is I-123 / I-133 that you wanted to inquire about. All sorts of iodine are taken up more in the thyroid. This is because the thyroid makes its hormone thyroxine from it, so it has a 'pump' to take it up easily.
Both I-123 and I-133 are used in radioactive iodine uptake(RAIU) scans. I-133 has a much longer life, and in addition to scans it is also used as a medicine to destroy overactive thyroids(when given in large doses). I-123 has a much shorter half life of nearly 14 hours, that means half of the dose of I-123 has been degraded in that time.
Please feel free to share with us the reports of your scan.
Regards and best wishes,
Dr. N. Haider

| Check a doctor's response to similar questions

Are you a Doctor, Pharmacist, PA or a Nurse?

Join the Doctors Lounge online medical community

  • Editorial activities: Publish, peer review, edit online articles.

  • Ask a Doctor Teams: Respond to patient questions and discuss challenging presentations with other members.

Doctors Lounge Membership Application

Tools & Services: Follow DoctorsLounge on Twitter Follow us on Twitter | RSS News | Newsletter | Contact us