Which blood group contains the least amount of H antigen?

The blood group that contains the least amount of H antigen is A1B. This is because individuals with the A1B blood type express A and B antigens on their red blood cells, which are derived from the H antigen. The presence of these antigens reduces the amount of unconverted H antigen on the red cell surface, as the H antigen is utilized in the formation of A and B antigens.

In contrast, other blood types like A2, B, and A1 typically have a higher expression of H antigen because the conversion to A or B antigens can vary significantly among individuals. A2 and B groups do retain more H antigen compared to A1B, as they can have different amounts of A or B antigen present without utilizing all available H antigen for conversion.

Thus, A1B has the least amount of H antigen because the high expression of A and B antigens on these red blood cells leads to minimal residual H antigen.