Changing practice: red blood cell typing by molecular methods for patients with sickle cell disease

Abstract

Background: Extended red blood cell (RBC) antigen matching is recommended to limit alloimmunization in patients with sickle cell disease (SCD). DNA-based testing to predict blood group phenotypes has enhanced availability of antigen-negative donor units and improved typing of transfused patients, but replacement of routine serologic typing for non-ABO antigens with molecular typing for patients has not been reported.

Study designs and methods: This study compared the historical RBC antigen phenotypes obtained by hemagglutination methods with genotype predictions in 494 patients with SCD. For discrepant results, repeat serologic testing was performed and/or investigated by gene sequencing for silent or variant alleles.

Results: Seventy-one typing discrepancies were identified among 6360 antigen comparisons (1.1%). New specimens for repeat serologic testing were obtained for 66 discrepancies and retyping agreed with the genotype in 64 cases. One repeat Jk(b-) serologic phenotype, predicted Jk(b+) by genotype, was found by direct sequencing of JK to be a silenced allele, and one N typing discrepancy remains under investigation. Fifteen false-negative serologic results were associated with alleles encoding weak antigens or single-dose Fy(b) expression.

Conclusions: DNA-based RBC typing provided improved accuracy and expanded information on RBC antigens compared to hemagglutination methods, leading to its implementation as the primary method for extended RBC typing for patients with SCD at our institution.

Fig. 1.

Comparison of DNA-based RBC typing with serologic typing. (A) Prevalence of RBC antigens predicted by genotyping in a cohort of patients with SCD (n = 494) compared to reported prevalence determined by serologic typing for black and Caucasian populations in Reid et al. *Antigens for which the frequency between Caucasians and patients with SCD had a p value of less than 0.0001. (B) Seventy-one total discrepancies out of 6360 antigen result comparisons between serologic and genotype predicted results. Bars indicate number of serologic discrepancies per antigen for which repeat serologic testing confirmed the genotype result in all but two cases. Not discrepant indicates the two repeat serology results that were consistent with the historical serologic record.