Q.What is Rh factor?

Human red blood cells carry genetically determined surface antigens defining several blood-group systems, of which ABO and Rh are clinically most important.

The ABO system, discovered by Karl Landsteiner (1900), rests on two RBC-surface antigens, A and B, and their matched serum antibodies ('a' and 'b'): group A (antigen A, antibody b), group B (antigen B, antibody a), group AB (both antigens, no antibodies — the universal acceptor, since it has no antibody to react against a donor's antigens) and group O (no antigens, both antibodies — the universal donor, since it carries no antigen for a recipient's antibodies to attack). Donor-recipient compatibility follows directly: O can donate to all groups, AB can receive from all groups. …