Anti-Jr(a) antibodies are generally composed of Immunoglobulin G and develop when individuals are exposed to Jr(a) positive blood through pregnancy or blood transfusion. Some cases of anti-Jr(a) have been reported in patients who have not been previously transfused or pregnant. Jr(a) is more strongly expressed on cord blood cells than on adult red blood cells, and anti-Jr(a) has been reported to cause hemolytic disease of the newborn (HDN), including fatal cases of HDN. The antibody has also been implicated in delayed hemolytic transfusion reactions. However, the clinical significance of the antibody is variable: in some cases, individuals with anti-Jr(a) have been transfused with Jr(a) positive blood or given birth to Jr(a) positive babies without incident. It is recommended to transfuse individuals with anti-Jr(a) with Jr(a) negative blood if the antibody titer is high. In other cases, "least incompatible" blood (the blood unit that gives the weakest reactions during crossmatching) may be suitable. It is difficult to secure Jr(a) negative donor blood due to the rarity of this blood type. ABCG2 is a uric acid transporter, and the Jr(a) negative phenotype is associated with gout in Japanese populations.
Junior blood group system
Augustine blood group system
Sid blood group system
Vel blood group
Rh blood group system
P1PK blood group system
Lan blood group system
Indian blood group system