Answer:
Anti-Kpa is an antibody formed in response to exposure to the Kpa antigen through pregnancy or transfusion. Kpa is also known as Penny-a, and is in the Kell blood group system. It is known as a low-frequency antigen because it is only found in around 1-2% of the population. The other Kell blood group system antigens include Kell (K), Cellano (k), Penny-b (Kpb), Sutter (Jsa), and Matthews (Jsb).