A case of possible 'auto'anti-D during pregnancy?

A senior technologist at a hospital in Ontario, Canada reports that his hospital transfusion service is currently following a 37-year-old group B, Rh positive woman who at the time of this posting is in her first trimester of pregnancy. The patient has had multiple pregnancies with no history of alloantibodies or autoantibodies, and no history of transfusions or Rh immune globulin injections. Her most recent antibody detection test using EDTA plasma and a GEL-antiglobulin method reacted 1+, and a panel work up revealed anti-D.

The Canadian transfusion service believes her anti-D is an autoantibody for the following reasons:

1. She has a 'microscopic' positive direct antiglobulin test (DAT) result when testing by a manual tube method, but a 2+ DAT result when testing by a GEL-antiglobulin method. Her DAT for cell bound C3b,d is negative when testing by tube method.

2. An eluate shows anti-D that is strongly positive with D+, LW(a-b-) cells. The eluate is negative with umbilical cord Rh negative cells and all other Rh negative cells that were tested. Unfortunately there was insufficient plasma sample to test umbilical cord cells that were LW-.

3. The patient's serum antibody reacts 3+ to 4+ with D+ ficin treated cells in a GEL-antiglobulin test.

4. Her anti-D has a titer of 1. This institution reports titers as the last +/- reaction (microscopic).

5. The patient has not been infused with any globulin product at any time and is reportedly on no medications.

The attending physician is inquiring as to any experience with such a case. The inquiring colleague's transfusion service will continue to monitor the titer of the anti-D throughout the pregnancy as well as test for hemolysis.

The following comments were received.

1. In response to the above case description, an experienced immunohematologist in Michigan comments that this is indeed an interesting case, and that it is appropriate to monitor this antibody during pregnancy. He also suggests that the woman's Rh genotype be determined using molecular analysis, to ensure that her RHD gene is normal, just in case she is not a partial D (e.g., DIII) who is beginning to make a allo anti-D with an autoantibody component. He would also suggest an autoadsorption-elution study to show if Rh-negative red cells can adsorb and then elute this antibody.

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