In performing titration studies for NON-Rh antibodies in pregnant women, what is the practice regarding selection of reagent red cells that are heterozygous vs homozygous for the antigen in question?

A blood banker in Cleveland would like to survey the e-network regarding the selection of reagent red cells used for titration studies when working up antibodies OTHER THAN anti-D. For example, based on the recent e-Network discussion, the community norm for titrating anti-D seems to be the use of R2R2 red cells. However, what do colleagues use for other non-Rh alloantibodies such as Kell, Duffy, Kidd, etc when titering for potential HDN. The inquiring blood banker's laboratory uses red cells from individuals who have a heterozygous expression on their red cells of the corresponding antigen. Is this the standard practice?

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The following responses were received.

ADDENDA Jan. 9, 2003

1. An expert immunohematologist in Michigan (who the Editor believes is still amazed that Ohio State actually beat Miami in the Fiesta Bowl) is of the opinion that it probably does not matter if one uses homozygous or heterozygous red cells for specific antigens, when performing titrations of antibodies capable of causing HDN. His opinion is based on data that his group has generated over the past few months, when using cells that are from heterozygotes or apparent homozygotes. He acknowledges that some workers elect to use cells with a single dose antigen expression, since such cells reflect the phenotype of fetus. Others prefer to err on the side of safety and use apparent double dose red cells. He says that we need to keep in mind that (apart from one report on anti-Fy(a) in pregnancy) the only data we have regarding the utility of antibody titration in monitoring for HDN are from pregnancies affected with anti-D, and (surprisingly) it is not clear what Rh phenotypes were used by the early investigators who promoted the concept of a critical titer. Further, current technologies permit monitoring for HDN by non-invasive means, and could ultimately eliminate the need for prenatal antibody titers.
   
   That being said, he is of the opinion that we need to be both consistent and practical in our selection of RBC phenotypes used for titration studies, and we need to have a discussion with our obstetricians as to how they plan to use the results in the absence of any data regarding the significance of these titration studies. In Michigan, they have traditionally used single-dose RBCs for non-Rh antibodies, but have now considered switching to double-dose RBCs, if practicable, to be consistent with their policy for titration studies of anti-D. However, their data to date show that while titration "scores" (sum of reaction scores for all positive dilutions) are often higher with double-dose cells than with single-dose cells, the "titers" (reciprocal of highest dilution yielding a macroscopic 1+ reaction) are the SAME regardless of dosage. He adds that when multiple antibodies are present, consideration should be given to using a single cell sample carrying all antigens to which the patient has made antibodies, rather than titrate each antibody separately, since the "cumulative" antibody titer will most likely reflect the need to monitor for HDN by other means.

ADDENDA Dec. 21, 2005

2. A Technical Support Officer of the New Zealand Blood Service would like to know if after three years have passed, if the expert immunohematologist in Michigan who shared his opinion above still believes that ".....consideration should be given to using a single cell sample carrying all antigens to which the patient has antibodies, since the 'cumulative' antibody titer will most likely reflect the need to monitor HDN by other means." She wonders if in 2006 the practice of using a single cell sample for titration of multiple antibodies will be more popular. She is interested in feedback from those who have experience with this testing strategy and/or who have strong views either way as to its merits. Is the approach different depending on the antibodies involved i.e. for Rh; Rh and non-Rh; or non-Rh antibody mixtures only?
   
   
3. The Michigan Immunohematologist responds that as 2005 comes to a close there seems to be less reliance on titers in the management of HDF/Newborn. That said, he maintains that the titration, if done, should use red cells that carry all of the antigens to which the maternal serum contains antibodies, unless the father (and in his pessimistic opinion, the certainty of paternity is only 90% in most instances) is known to lack the corresponding antigen. The only exception is with apparent anti-C+D in a D- woman who has received all required doses of RhIG. If the titer vs. r'r cells is equal to or greater than that vs. R2R2 cells, than anti-D may not be present and the woman is a candidate for RhIG therapy. (Please see the recently published AABB Practice Guidelines on Prenatal/Perinatal Testing.) He adds that of particular concern is the situation where a woman has anti-c and anti-E, where the titers vs. c+E- and c-E+ are low, but the titer vs. c+E+ is high due to the presence of anti-cE. Similarly for anti-C and anti-e and anti-Ce. Professor Judd concludes by acknowledging that he knows not what others are doing!

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