The significance of the weak D phenotype in blood banking is as follows:
Weak D as a blood donor: As donors, weak D red cells are considered to be Rh(D)-positive because, even though the D antigen is weak, it is present. If weak D red cells were transfused to D-negative patients, the patients might be immunized to produce anti-D. Some blood transfusion services give weak D donors the designation "Rh positive, weak D."
Weak D as a blood recipient: As recipients, patients with the weak D phenotype are considered to be Rh(D)-negative, and usually receive only Rh(D)-negative red cells. This is because a mosaic-type weak D such as DAB might produce anti-D (anti-DCD) if given DABCD red cells from a normal Rh(D)-positive donor (although this is unlikely). Note: If a weak D person phenotypes as Rh(D)-positive, Rh(D)positive donor cells would be transfused.
Weak D as it relates to prenatal testing: An Rh(D)-negative woman is given Rh immune globulin if she has an Rh(D)-positive infant and has not produced active anti-D. Rh immune globulin may also be given if the Rh(D)-negative woman has a weak D positive infant because weak D red cells can theoretically cause the production of anti-D, although how often this happens is uncertain (and likely rare).
Policies for typing pregnant women for weak D (Du) vary according to country and the protocols for administering Rh immune globulin. For example, in the USA the Standards of the American Association of Blood Banks (AABB) specifies that pregnant women who appear to be Rh negative should be tested for weak D; if Rh positive or weak D, they are considered to be Rh positive and are not candidates for Rh immune globulin.
In contrast, the Standards of the Canadian Society for Transfusion Medicine (CSTM) do not require weak D typing for pregnant women. If Rh negative or weak D such women are candidates for Rh immune globulin. Although extremely rare, weak D persons of the mosaic type can theoretically produce anti-D.
The need to do weak D testing of newborns who type as Rh negative and are born to Rh negative females is universally accepted. A weak D test on the infant is required since mothers will receive Rh immune globulin if the child is weak D. (Some labs may not do a Du test on apparently Rh negative infants if they are using anti-D antisera that is potent enough to detect the weak D phenotype without doing a Du test.)
|Significance in Blood Banking|