During times of critical blood shortages, performing the serologic weak D test with reflex to molecular testing may assist in the retyping of the Rhesus (RhRh factor A protein or antigen found on red blood cells. When an Rh-negative mother carries an Rh-positive fetus, her immune system may make antibodies that attack the fetus' red blood cells.) D status of patients, according to findings from an analysis published recently in the American Journal of Clinical Pathology.
The serologic weak D test has the ability of identifying Rh(D) variants, including weak D types 1, 2 and 3, and thus establish whether a patient with hemolytic disease of the fetus and newborn (HDFN) might be at risk for hemolytic transfusion reactions.
Partial D and weak D both are terms used in the realm of blood typing. They refer to variations in the Rh(D) antigen on red blood cells (RBCs).
Importance of the Rh antigen group in transfusion medicine
In the field of transfusion medicine, the Rh antigen group is critical because of its high polymorphism (that is, the presence of the highly polymorphic RHD and RHCE genes) and strong immunogenicity.
This means that if an individual who is deficient in the Rh antigen is exposed to Rh-positiveRh-Positive A blood type trait that means your red blood cells have the Rh(D) antigen. blood, the body will most likely generate antibodiesAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. against it, which can potentially lead to such severe events as HDFN in Rh-negativeRh-Negative A blood type trait that means your red blood cells lack the Rh(D) antigen. pregnant patients.
Read more about the testing and diagnosis of HDFN
More about the D antigen
The D antigen contains numerous epitopes with several variations. Epitopes are described as small sites on the surface of an antigen to which antibodies can bind.
Variations on the D antigen include weak D, in which decreased expression is observed, and partial D, in which the loss of certain epitopes is reported.
Both weak D and partial D can lead to potential exposure to the risk for alloimmunizationAlloimmunization When a person’s immune system develops antibodies against foreign antigens from the same species—such as when an Rh-negative mother’s body forms antibodies against her baby’s Rh-positive red blood cells., based on the subtype of the Rh(D) antigen that is involved.
In what situations is serologic weak D testing performed?
Serologic weak D testing, which is followed by molecular testing, is performed in blood donors who test negative the Rh(D) antigen.
This method of testing is also used in newborns who are typed negative for Rh(D) and are born to Rh(D)-negative mothers.
Importance of understanding patients’ genotypes regarding weak D or partial D
Because of currently reported shortages of blood supplies, an understanding of weak D or partial D typing can play a key role in managing limited RBC supplies currently being reported in blood banks.
In the present study, the researchers sought to further portray individuals who initially type negative for Rh(D) but type positive for weak D via molecular testing. They aimed to evaluate risk for alloimmunization, retype the Rh(D) findings, and prevent the unnecessary usage of Rh(D)-negative RBC units during times of critical shortages.
How was the study conducted?
Over a four-week period in December 2023, the investigators obtained the results of ABO/Rh(D) blood typing among patients with negative Rh(D) test results but positive weak D test findings.
In all participants, D-variant molecular testing was performed by a reference laboratory.
What were the results of the study?
Initially, three individuals tested negative for Rh(D) but positive for weak D. Two of these patients exhibited a genotype that was indicative of the presence of weak D-positive type 1.
Such individuals with weak D-positive type 1 are able to receive Rh(D)-positive RBC units, as they are not at risk for alloimmunization and development of anti-D.
The third participant exhibited a genotype indicative of the presence of partial D antigen. Such individuals should receive Rh(D)-negative RBC units, as they are considered to be at risk for alloimmunization and development of anti-D.
The authors concluded that “Although the vast majority of Transfusion Medicine services do not perform the serologic weak D test with reflex to molecular testing, characterizing patients who test negative with initial serologic Rh(D) testing…may aid in retyping the Rh(D) of patients during critical shortages, particularly for patients with ABO blood groupBlood group A classification of blood based on inherited markers found on red blood cells. The ABO and Rh blood groups are most common in HDFN. O.”
