Management of a pregnant woman who may have native anti-D, but has also received an antepartum dose of RhIG

A transfusion service laboratory technologist in the Heartland of America reports that her blood bank is aware of an OB patient (about 28 weeks gestation) who refused RhIG after her most recent delivery of an Rh-positive baby, and subsequently developed anti-D. The patient's anti-D titer 6 weeks ago was <1 using a saline-antiglobulin (IgG) tube method with 60 minutes incubation. Last week, however, the patient's anti-D titer increased to 8, which prompted a phone call to the patient’s physician who acknowledged that the patient had received IM RhIG earlier that day, prior to collecting the sample with the anti-D titer of 8. The blood bank is now trying to determine how best to follow this patient’s anti-D titers (if at all), given that the patient is already alloimmunized with anti-D, but recognizing that the patient just received a full dose of RhIG. The inquiring colleague is looking for advice as to the time frame others would suggest for collecting future titration samples? In addition, any advice or guidelines on clinical management of this patient would be appreciated.

The following comments have been received.

1. In response to the above query, Dr. Willy A Flegel of the University of Ulm (attribution used with permission) suggests checking the patient's anti-D titer regularly, for instance every 14 days, making sure to compare the current titer with the previous (or initial) titer by doing both titrations simultaneously (using the current sample and a thawed serum sample from the previous or initial sample). This approach will allow for a direct comparison of the titers. He comments that injected (passive) anti-D should appear rapidly in the circulation and stay there for at least several weeks. However, he believes that after the injected anti-D reaches its peak blood level, one would expect the anti-D titer to fall, unless the patient begins to make her own native anti-D. If the patient's anti-D titer stays up and begins to increase, this would mark the likely beginning of secondary anti-D alloimmunization. In terms of clinical follow up, he suggests that if clinically significant anti-D production is suspected, emerging fetal anemia could be checked (in his opinion) least invasively by ultrasound. In his view, amniocentesis should be avoided. If fetal DNA sampling is necessary, it is now possible to perform DNA testing of a fetus using a peripheral blood sample taken from the mother. Dr. Flegel wonders about the Rh status of the current father, who could be tested for Rhesus homozygosity.

Please submit comments to the e-Network Forum.

Ira A. Shulman, MD
CBBS e-Network Forum Editor & Moderator