Crossmatching helps identify immunological (antigen-antibody) incompatibilities between a donor and a recipient:
The major crossmatch test combines the donor's erythrocytes with the recipient's plasma (or serum) to assess for the presence of recipient alloantibodies that will destroy the donor's RBCs.
The minor crossmatch test combines the donor's plasma (or serum) with the recipient's RBCs, assessing for the risk of transfusing alloantibodies from the donor that will destroy the recipient's RBCs.
Crossmatching can be performed in reference laboratories or in clinics manually using a tube or slide method. Point-of-care gel and immunochromatographic commercial crossmatch options are also available and have variable reported agreement with laboratory methods.
Incompatible donor-recipient pairings result in agglutination and entrapment of RBCs within the gel matrix or on the immunochromatographic membrane, signifying a positive (incompatible) reaction (see gel crossmatch test image).
Courtesy of Dr. Shauna Blois.
Crossmatching is not required before a first transfusion in a dog, due to the lack of naturally occurring alloantibodies (NOAbs), but is strongly recommended > 4 days after a subsequent transfusion.
Due to the presence of highly immunogenic NOAbs in cats, major crossmatching is strongly recommended both before a first transfusion in cats and then > 2 days after any subsequent transfusion.
