This test identifies normal RHD-positive, RHD-negative, RHD variant alleles, and normal RHCE alleles (C, c, E, e, Cw).
In addition to the RhD-positive and RhD-negative phenotypes, RHD variant alleles can occur. These RHD variant alleles result in variable expression of the RhD antigen; therefore individuals with RhD variant expression can develop alloanti-D. RHD variant alleles occur in all populations, however most commonly occur in individuals of African origin.
RhD variants are most commonly expressed as the result of single nucleotide polymorphisms or hybrid RHD-RHCE alleles; produced by gene conversion events between the highly homologous RHD and RHCE genes on chromosome 1p34-p36.
A wild type RHD gene can be distinguished from the most common RHD variant alleles by molecular detection of the different exons and mutations of the RHD gene, using SSP-PCR. This test also the detection of normal RHD, the most common and important RHD variant alleles; it also allows detection of the C, c, E, e and Cw antigens and the allelic variants RHD*08N.01 [RhDΨ] and RHCE*01.20 [r’S].
Patients who may benefit from RHD/RHCE genotyping include:
- Transfused patients where determination of RhD and RhCcEe group by phenotyping is not reliable.
- RhD-positive individuals with certain variant RHD/RHCE genes who may produce alloanti-D
- Patients where it is unclear if they have auto or alloanti-D
Patients of African origin in which RHD variant genes are more common If an RHD variant allele is detected in a patient of African origin, then an RHCE Variant investigation is usually also indicated. The RHCE Variant Investigation is an additional test and would incur an additional charge.