The June 2024 issue of the journal Immunohematology published a literature review of the current benefits and usefulness of molecular genotyping in transfusion medicine.1 The emergence of molecular testing in recent years has advanced patient care in many different fields of medicine, with transfusion medicine being no exception. Red blood cell (RBC) genotyping uses molecular methods to predict the expression of blood group antigens by interrogating for known genetic polymorphisms as defined by the International Society of Blood Transfusion (ISBT). The use of RBC genotyping in addition to standard serologic techniques can prove to be a useful tool to the blood bank and clinicians in donor testing, prenatal testing, and recipient testing including complex antibody workups. There are two FDA-approved genotyping methods, PreciseType HEA by the Immucor unit of Werfen and ID CORE XT by the Progenika Biopharma unit of Grifols.
Recipient Testing
The use of RBC genotyping can prove useful in several ways in pre-transfusion testing. Obtaining a serologic phenotype in a recently transfused patient is often difficult or impossible to perform without reticulocyte separation using microhematocrit centrifugation. RBC genotyping can be utilized to obtain a predicted phenotype in a multiply transfused patient. In addition, RBC genotyping can be beneficial in predicting a phenotype in a patient who presents with a warm autoantibody or a positive direct antiglobulin test (DAT) or in cases where commercial antisera are not available for testing. Genotyping can be particularly useful if a suspected antibody is directed toward a high-prevalence antigen. Patients receiving monoclonal antibody therapy often present with serologic interference, and molecular testing can be successfully used in these patients to predict RBC phenotypes.
Donor Testing
Donor center laboratories are often responsible for testing and providing antigen-negative RBC units. Matching for C, E, and K antigens has become a common practice in multiply transfused patients to prevent alloimmunization. Chronically transfused patients with alloantibodies, such as those with sickle cell disease (SCD), require antigen-negative blood for transfusion. There is a high rate of alloimmunization among patients with SCD despite being matched for Rh and K antigens, believed in part to be due to the inability of standard serologic phenotyping techniques to detect variant antigens in the Rh system. Molecular testing of donor units can help provide more accurate Rh antigen matching for a patient at risk of developing an antibody to a variant antigen.
Prenatal Testing
There are two main applications of RBC genotyping in prenatal testing. These are predicting hemolytic disease of the fetus and newborn (HDFN) and determining the need for Rh immune globulin (RhIG) in a pregnant patient with a weak or partial D antigen. The most common causes of HDFN are alloimmunization to D and K. If the mother is negative for D, genotyping can be performed on the father to determine his zygosity for the RHD gene. If the father is homozygous, the fetus will be D+ and potentially develop HDFN; if the father is heterozygous, then the fetus only has a 50% chance of inheriting the D antigen and half the risk of HDFN. Molecular genotyping can also help avoid administering RhIG to mothers who are not candidates. If the initial Rh testing indicates that the mother has a weak D or a D typing discrepancy, molecular testing is needed to determine if the patient is at risk for developing allo-anti-D and therefore help determine if she is a candidate for RhIG.
In summary, the use of RBC genotyping is a useful supplementary tool in the blood bank. In certain situations, molecular testing can provide valuable information that cannot be obtained through standard serologic methods. As with any method, molecular testing does have some limitations, including test availability, false positive or negative reactions, turnaround time, and cost. However, despite its limitations, RBC genotyping has proven useful in increasing availability of antigen-negative red blood cells and otherwise advancing patient care.
RBC genotyping is available from the American Red Cross National Molecular Laboratory.
Reference
1. Akinbolaji TJ. When and why is red blood cell genotyping applicable in transfusion medicine: a systematic review of the literature. Immunohematology 2024;40:58–64. DOI: 10.2478/immunohematology-2024-009.
