There are four possible combinations of blood types in the parents of AB children: two ABs, one A and one B, one AB and one A, and one AB and one B. The blood type of the parents of an AB child is a genetic trait expressed in the form of antigens on the surface of the blood components.
Human blood type is a genetic trait expressed in the form of antigens on the surface of blood components, so the results of the assay depend mainly on the type of antigens on the surface of the red blood cells, which are related to the ABO allele and have a certain pattern of inheritance.
There are four ways of combining the blood types of the parents of AB children. The blood types of the parents of AB children may be that both of them have AB blood, one of the parents is A and one of the parents is B, one of the parents is AB and one of the parents is A, and one of the parents is AB and one of the parents is B.
The exact blood type of the parents of an AB child requires blood typing, and can also be categorized as Rh-positive or Rh-negative based on the presence or absence of the D antigen.