A type-A Rh-negative infant has spherocytes on his blood film and a weakly positive direct antiglobulin test. What antibody will most likely be found on the infant's red cells?

a. IgG anti-A antibody
b. IgM anti-A antibody
c. D antibody
d. Kell antibody

ANS: A
This occurs in infants whose mothers make an IgG anti-A (in this case) or anti-B at a low level. The disease is usually mild because most ABO antibodies are IgM and do not cross the placenta because of their large size.