What is the most likely reason for an ABO discrepancy observed in this blood group testing?

The most likely reason for an ABO discrepancy in blood group testing being attributed to the presence of anti-H is based on the fundamental role that the H antigen plays in the ABO blood group system. The H antigen is the precursor for the A and B antigens; therefore, if an individual has anti-H antibodies, they would react against the H antigen found on red blood cells, which may lead to an unexpected typing outcome. This can present as a discrepancy, especially in individuals where the presence of the A or B antigens is not detected due to the anti-H antibody interfering with the expected reactions.

In specific populations, such as those with Bombay phenotype (Oh), individuals may lack functional H antigen entirely, resulting in the production of anti-H antibodies. When utilizing standard ABO testing, this can result in unexpected group results since the antibodies would agglutinate the cells that would otherwise showcase the A or B antigens.

It is crucial to recognize that other scenarios, such as the presence of unexpected antibodies, rouleaux formation, or anti-A1, can also result in discrepancies, but they typically present in contexts where the existing A or B antigens are not recognized or where nonspecific reactions may occur. The presence of anti-H is distinctly significant in interpreting