Background/Case Studies: The RHD and RHCE genes are known for their genetic diversity, which results in expression of weakened and partial antigens that cannot be identified by serology. Given the potent antigenicity of RH antigens, correct identification is crucial .
Study
Design/Methods: We present three cases investigating the diagnostic value of RHD/RHCE genotyping.
Case 1: The individual expresses a weak D allele and is unlikely to form anti-D antibodies upon exposure. Weak D patients can be identified by serology but are difficult to distinguish from partial D patients, who are highly capable of generating anti-D antibodies. Genotyping is critical to avoid unnecessary use of RHD negative RBCs in weak D patients.
Case 2: The individual expresses a partial D allele and can produce anti-D antibodies. The patient also possesses two variant RHCE alleles, which express partial c and e antigens, and a low incidence antigen known as Crawford (RH43). As with RHD, individuals who express only partial RHCE antigens can make antibodies when exposed to the normal proteins. Thus, this patient could make antibodies to all four of the common RHCE antigens (C, c, E, e), leading to the necessity for RHCE null or genotype matched RBCs for transfusion. Furthermore, the Crawford antigen can cross-react with some monoclonal anti-D reagents, potentially leading to incorrect serological designations of RHD positivity in RHD negative, Crawford positive patients if genotyping is not performed.
Case 3: The individual expresses two partial RHD alleles and can produce anti-D antibodies. The RHD*04.01 allele also generates an antigen known as Goa (RH30), which can stimulate antibody production in Goa- individuals. This allele is found in approximately 3% of African Americans, so Goa antibodies are sometimes encountered in previously transfused patients. Given that Goa antisera are not commonly available, genotyping is critical for identifying Goa negative units for these patients.
c. Methods
RHD/ RHCE genotyping was performed using RBC-FluoGene CDE eXtend (inno-train). The kit is a real-time PCR assay based on the TaqMan probe technique. It comprises 43 RHD and 30 RHCE SNPs. FluoGene software was used for analysis.
Results/Findings: In all three cases, the genotyping results extend and clarify serological findings, allowing selection of safer RBC units for transfusion. Sample 1 was found to carry a weak D type 1 allele. The RHD and RHCE alleles for sample 2 could be specified, and in sample 3 partial DIVa was confirmed. Detailed results will be supplied on the poster.
Conclusions: RH genotyping using the CDE eXtend assay permits simultaneous RHD and RHCE genotyping, thereby optimizing workflow and permitting more accurate prediction of alloimmunization risks. As such, it increases transfusion safety in populations known to carry RHD and RHCE variants and enables more efficient blood supply utilization.
