Which antibodies will be detected in the serum of a Bombay genotype?

• A. anti-A
• B. anti-B
• C. anti-H
• D. anti-A, anti-B, anti-H

Answer: (D)

The key idea is the Bombay phenotype (hh): these red cells lack the H antigen, which is the precursor needed to form A and B antigens. Without H, A and B antigens can’t be expressed, so individuals with this genotype do not present H, A, or B on their own red cells. Their immune system recognizes all three of these as foreign and makes antibodies against them. Hence, their serum contains anti-H as well as anti-A and anti-B antibodies. In other words, antibodies against H, A, and B are detectable. This also explains why someone with the Bombay phenotype can only receive hh (Bombay) blood, since other blood types carry H antigen.