The Timing of Pregnancy Testing in ¹³¹I Therapy

TO THE EDITOR: In the publication of the SNMMI guideline on ¹³¹I therapy (1), there appears a recommendation for a pregnancy test to be performed within 24 h of the administration of ¹³¹I for women of reproductive age who cannot provide written documentation of a hysterectomy or bilateral salpingo-oophorectomy.

Some readers have raised the concern that if the pregnancy test is obtained some hours before the suggested 24-h limit and a false-negative result ensues, they would be liable for a lawsuit. We must emphasize that a guideline is not a regulation and has no force of law.

It is simply a fact that pregnancy tests are negative until implantation of the embryo, which occurs 7–10 d after fertilization. Therefore, a test performed 48 h before therapy will miss more pregnancies than one performed at 24 h or on the same day, and it seems unreasonable to take that chance.

At the University of Cincinnati Medical Center, we draw blood for a β–human chorionic gonadotropin study on the day of therapy, the results of which will be returned in 30 min. Meanwhile, the nuclear pharmacy will not deliver the prescribed activity for 90–120 min, so no one is inconvenienced, and the patient is protected to the best of our ability from being treated while pregnant.

• © 2013 by the Society of Nuclear Medicine and Molecular Imaging, Inc.