Comparison of Fy(b) status as determined serologically and genetically

Comparison of the serologically determined phenotype and the genotype of samples as defined by PCR-RFLP indicated a significant percentage of discrepancies on analysis of serologically defined Fy(a + b-) samples. An investigation of these discrepancies has shown that the serologically determined phenotype of the samples varies with respect to the reagent used but that the PCR-RFLP assay gives reliable results for all the samples investigated. The samples which yielded the discrepant results were further investigated and the results indicated weakened expression of the Fyb antigen. This may arise by a method similar to the expression of Fyx although we found the incidence of these samples to be much higher than that reported for Fyx. These results may have important implications for the routine testing of blood donations, particularly in situations where the unit is to be transfused to a patient who has previously formed an anti-Fyb.