PARABOMBAY PHENOTYPE -A RARE CASE REPORT

The H antigen is the precursor for the formation of A and B antigens and its absence is termed as H antigen deficient phenotype. It results in, Bombay or Para-Bombay blood group in an individual. If H antigens are not expressed on both RBCs and secretions, then the resultant blood group is a Classical Bombay phenotype with anti-H antibodies in their serum. If H antigens are adsorbed from the plasma of the secretors and insufficiently present on RBCs, the resultant weak H antigen is termed as Para-Bombay. Genetically Para-Bombays lack an active H allele (their genotype is hh) but carry at least one Se (Secretor gene) allele.Para-Bombay or red blood cell (RBC) H negative secretor individuals, having weak or absent anti-H activity, may remain undetected on routine blood grouping, as is illustrated in the following case.CASE REPORTA blood sample of a 62-year-old male patient was submitted to the Blood Bank for blood grouping. In forward grouping, no agglutination was observed with A, B and AB antisera and agglutination was noticed with D antiserum. In reverse grouping, there was agglutination in tube labeled B cells and no agglutination in tubes A cells and O cells resulting in discrepancy between forward and reverse grouping. H antigen was absent on RBCs as there was no agglutination with anti-H antiserum. These findings suggested that the individual's blood group belongs to Para-Bombay A (Para-AH) phenotype, which is a rare entity.CONCLUSIONIf there is a discrepancy between forward and reverse grouping suggestive of para- Bombay phenotype, always use anti-H lectin in the forward grouping. If facilities are available, exact phenotype of para-Bombay blood group can be diagnosed by assessing the secretor status of the individual and molecular genotyping.