An investigation of secondary anti-D immunisation among phenotypically RhD-negative individuals in the Chinese population

Abstract

Background: Despite the introduction of anti-D prophylaxis into clinical practice, RhD alloimmunisation remains a problem, particularly in the context of transfusions and pregnancy-induced alloimmunisation. The incidence of RhD alloimmunisation among phenotypically RhD-negative individuals is unknown in most countries. We investigated RhD alloimmmunisation in RhD-negative pregnant women and transfusion recipients in south-east China in order to optimise the prevention of this phenomenon.

Methods: We analysed the RhD alloimmunisation status of RhD-negative pregnant women and transfusion recipients in south-east China. The RhD blood types of the study population were identified by standard serological methods. The D antigen was further tested with the indirect antiglobulin test to exclude or confirm weak D or partial D types. RhC, c, E and e antigens were typed in all subjects. If anti-D antibody screening was positive, the specificity and titre of the antibody were determined. The Del phenotype was investigated by the polymerase chain reaction sequence-specific primer method.

Results: An anti-D antibody was found in 61 of 416 RhD-negative pregnant women (14.66%), and in 11 of 227 RhD-negative transfusion recipients (4.85%). None of the 72 RhD-negative pregnant women or transfusion recipients with anti-D had the Del phenotype. Anti-D antibodies were not detected among Del phenotype individuals and Del phenotypes were not found in anti-D antibody producing individuals.

Discussion: Our study suggests that the risk of alloimmunity-induced neonatal haemolysis increases in true RhD-negative multipara. Perinatal protection would be necessary in these patients, while antenatal anti-D testing and Rh immune globulin prophylaxis would be unnecessary for RhDel pregnant women. Pregnant women and transfusion recipients with the Del type seldom produce anti-D antibody. RhD-negative recipients are not at risk of alloimmunisation after transfusion with Del red blood cells.

Figure 1

PCR-SSP for RHD1227A (109 bp band). Lanes 1–4, 6–9, RHD1227A allele detected in Del phenotype samples; Lane 5, non- RHD1227A allele gene detected in Del phenotype samples; lane 10, Rh-negative control sample; lane 11, sample with a normal RHD gene; lane 12, H₂O control. A representative example of 155 Del phenotyped cases is shown.

Figure 2

Sequencing analysis of the RHD1227A allele. The arrow indicates the position of the nucleotide mutation between RHD exon 9 and intron 9. A representative example of 151 RHD1227A genotyped cases is shown.