If you recall, recently an e-Network member asked for opinions regarding antibody detection testing practices for Rh negative pregnant women who have received Rh Immune Globulin (RhIG). According to the inquiring member, at her facility antibody detection testing occurs for Rh negative prenatal patients at various points during the pregnancy, including at 34-36 weeks gestation. The member is most nterested in knowing what others do for the 34-36 weeks gestation antibody screening, because this testing usually follows the administration of an antenatal dose of RhIG (which is ordinarily given at 28 weeks). According to this member, at her institution a negative antibody screening test result at 34-36 weeks gestation is rarely followed by a clinician ordering additional RhIG to be administered to the patient. The inquiring member is concerned that a negative antibody screen result at 34-36 weeks gestation following antenatal RhIG suggests that a patient has insufficient Rh Immune Globulin on board, and that such a woman may be at risk of Rh alloimmunization. On the other hand, since most of the time the physicians at her institution fail to act on a negative antibody screen result at 34-36 weeks, the inquiring member wonders if the antibody screen for Rh negative women at 34-36 weeks gestation could be eliminated. If that test were eliminated at 34-36 weeks, her institution would avoid detecting the numerous passive anti-D's that are often detected at 34-36 week gestation following a 28 week RhIG injection, and therefore fewer antibody identification work ups would need to be done. The member comments that the AABB has no guidelines regarding this situation, nor is she able to resolve this issue by reading the report of the scientific section of the AABB regarding prenatal and perinatal immunohematology: recommendations for serologic management of the fetus, newborn infant and obstetric patient (Transfusion Vol. 30, No 2- 1990).

The following replies were received in response to the above question:

1. A recognized American expert in pre-natal immunohematologic testing replied that to his knowledge there are no data to support the inquiring member's institutional practice of routinely testing for unexpected RBC alloantibodies at 34-36 weeks gestation. This expert suggested that a paper written by Ness and Salamon might be worth reviewing. The paper is entitled, "The failure of postinjection Rh immune globulin titers to detect large fetal maternal hemorrhages. Am J Clin Pathol 1986;85:604-6 (abstract).

This expert goes on to comment that one could argue that when RhIG is not detected at 34-36 weeks gestation following a dose of RhIG at 28 weeks, that the RhIG may have been adsorbed by the Rh-positive fetus. In this case the fetal cells would be coated with anti-D and presumably would not stimulate the mother to make her own anti-D. But, according to this expert, it's all a matter for conjecture!

2. A famous blood banker from New York commented that unexpected red cell antibodies detectable at 36-38 weeks, but not 28 weeks rarely, if ever, cause severe hemolytic disease of the newborn. This blood banker does not see the purpose clinically of such testing being done at 36 weeks gestation, and would instead recommend a maternal antibody screen at the time of delivery if the 28 week determination is negative. He concluded with the statement that "actually an antibody screen 6 months post-partum would be the most clinically useful determination in my opinion".

3. Finally, a blood banker who currently works in Texas commented that published prenatal screening guidelines and the manufacturer's package insert agree that the first prenatal screen for possible antibody formation should be done somewhere around 26 to 28 weeks gestation. This blood banker was unaware, until she read this e-network discussion, of anyone performing an antibody screen at 34-36 weeks gestation following a negative screen at 28 weeks, and she frankly does not know why an antibody screen would be done at that time. This blood banker believes that there is no need to repeat the prenatal screen at 34-36 weeks, if the screen is negative at 26-28 weeks in the pregnancy, but that it is appropriate to perform a screen at the time of delivery.

Please submit comments to the e-Network Forum.

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