Compatibility Testing

Compatibility testing is performed to determine if a particular unit of blood can be transfused safely into a certain patient.

This includes ABO-Rh blood typing, antibody screening (for unexpected red blood cell antibodies that could cause problem in the recipient), and cross-matching.

Antibody screening

Antibody screening

There are many antigens besides A, B, and Rh. However, neither the donor nor the recipient is tested routinely for these other antigens.

However, if a patient has had a previous transfusion or been pregnant, they may have developed antibodies to one of these other antigens. And the recipient may have a transfusion reaction.

The presence of such an antibody is determined by doing an antibody screening test by mixing the patient's serum with red cells of a known antigenic makeup.

Antibody screening is used to test:

1. Donor plasma to make sure no unexpected antibodies will be transfused. If these antibodies are present, they could attach to the recipient's cells cause a positive transfusion reaction.

2. Patient serum before transfusion to make sure patient has no unexpected antibodies to react with donor cells. In this case we do not want the recipient's antibodies to attach to the donor cells causing a transfusion reaction.

3. Maternal serum to make sure pregnant mother has no antibodies to react with fetal cells. Hemolytic disease of the newborn is caused by the mother's IgG antibodies crossing the placenta and attaching to the baby's red blood cells.

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There is no A or B antigen

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Rh Antigens

RHD gene determines the presence of a membrane spanning protein that confers D activity on the red cell.

The RHCE gene determines the C, c, E, and e antigens.

There are other antigens of the Rh blood grouping.

MNS system

The MNS system is a complex system of over 40 antigens.

The M, N, S, s, and U antigens are the most important antigens of the MNS system with regard to transfusion medicine.

Kell System

There are around nine antigens of the Kell system,

the most important K and k.

Duffy System

The antigens are Fya and Fyb.

Kidd System

The antigens are Jka and Jkb.

The Lewis System

The Lewis system antigens, Lea and Leb.

Lutheran System

There are around nine antigens of the Lutheran

system, the most important are Lua and Lub.

Other Blood Group systems

Cartwright System Diego System Xg System Scianna System Dombrock Blood Group System Colton System LW System Chido/Rodgers System Gerbich System Cromer System Knops System Indian System Ok System Raph System John Milton Hagen System GIL System Cost System Er System Vel System

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Enhancement media (LISS or albumin)

LISS (low ionic strength solution) is an enhancement media that composed of NaCl, glycine and phosphate buffer. This solution speeds up antigen antibody reaction.

Albumin: reduces zeta potential, bringing the RBCs closer together and enhancing agglutination.

The zeta potential (ζ-potential): indicates the degree of repulsion between adjacent, similarly charged particles ( between negatively charged RBCs)in a dispersion. For molecules and particles that are small enough, a high zeta potential will confer stability (no coagulation) i.e., the solution or dispersion will resist aggregation.

When the potential is low (like when using 22% Albumin enhancement media --- positive charge) , attraction exceeds repulsion and the dispersion will break (coagulation occur). So It increases antibody uptake and decreases incubation time

37˚C phase is required since IgG are warm acting antibodies.

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Anti-human globulin (IgG) enables red cells to cross-link so that agglutination is visible.

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If a clinically significant antibody is identified, only red cells negative for the relevant antigen will be selected for crossmatching and transfusion.

For example, if the antibody is anti-K, RBC of the appropriate ABO and Rh type will be tested with anti-K anti-serum and only K-negative red cells will be selected for transfusion.

For added safety, an AHG crossmatch is also performed For clinically insignificant antibodies.