Many genetically defined ABO subgroups exhibit characteristic flow cytometric patterns.
BACKGROUND
A flow cytometric method for detection of low levels of A/B antigen had been developed previously in our laboratory. The aim of this study was to investigate if this approach could be utilized to characterize different ABO subgroups and constitute a useful tool in a reference laboratory.


METHODS
Blood samples causing ABO discrepancies (n = 94) by routine serology were further analyzed by ABO genotyping and flow cytometry. To verify the specificity of the monoclonal anti-A and -B reagents and to establish normal flow cytometric patterns, samples from 80 blood donors with common phenotypes were also assessed.


RESULTS
Distinguishable flow cytometric patterns were detected for several subgroups but were more apparent for A(weak) (n = 80) samples than B(weak) (n = 14). Two subgroups, A(finn) (n = 11) and A(3) (n = 10) displayed diagnostic features and were used to establish reproduciblity over time and between donors. In general, the consistency within subgroups was remarkable. The allelic enhancement phenomenon was clearly visualized among A(x) samples (n = 10) where different alleles in trans resulted in high, low, or no A antigen expression. Nonsubgroup samples including O/A and O/B chimeras or A(h) and B(h) para-Bombay phenotypes displayed clearly distinguishable histograms. Samples from pregnant women (n = 10) displayed acquired A antigen loss, apparently accentuated during the third trimester.


CONCLUSIONS
Genetically defined ABO subgroups and other anomalous phenotypes displayed flow cytometric profiles that may contribute valuable information to the investigation of ABO discrepancies. We conclude that the presented assay may complement traditional serology and genetic analysis in the reference laboratory setting.
Clinical Immunology and Transfusion Medicine, University and Regional Laboratories, Region Skåne and Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, Lund, Sweden.
Annika K
AK
Hult
Martin L
ML
Olsson
D000017:ABO Blood-Group System / Q000032:analysis* / Q000145:classification / Q000235:genetics; D000328:Adult; D000483:Alleles; D001788:Blood Grouping and Crossmatching / Q000379:methods*; D015331:Cohort Studies; D005260:Female; D005434:Flow Cytometry / Q000379:methods*; D005838:Genotype; D006801:Humans; D011247:Pregnancy; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D009626:Terminology as Topic
D000017:ABO Blood-Group System