Systematic RHD genotyping in Brazilians reveals a high frequency of partial D in transfused patients serologically typed as weak D.

Background: The discrimination between weak D types and partial D can be of clinical importance because carriers of partial D antigen may develop anti-D when transfused with D-positive red blood cell units. The aim of this study was to determine by molecular analysis the type of D variants among Brazilian patients requiring transfusions with serologic weak D phenotypes.

Material And Methods: Samples from 87 patients (53 with sickle cell disease, 10 with thalassemia and 24 with myelodysplastic syndrome), serologic typed as weak D by manual tube indirect antiglobulin test or gel test were first RHD genotyped by using the RHD BeadChip Kit (BioArray, Immucor). Sanger sequencing was performed when necessary.

Results: RHD molecular analysis revealed 32 (36.8 %) variant RHD alleles encoding weak D phenotypes and 55 (63.2 %) alleles encoding partial D antigens. RHD variant alleles were present in the homozygous state or as a single RHD allele, one variant RHD allele associated with the RHDΨ allele, or two different variant RHD alleles in compound heterozygosity with each other in 70 patients, 4 patients and 13 patients, respectively. Alloanti-D was found in 9 (16.4 %) cases with RHD alleles predicting a partial D.

Discussion: The frequency of partial D was higher than weak D types in Brazilian patients serologically typed as weak D, showing the importance to differentiate weak D types and partial D in transfused patients to establish a transfusion policy recommendation.