Antibody Screen

More properly called the “antibody detection test,” the antibody screen (as most blood bank types call it) is a test used to demonstrate “unexpected (non-ABO) antibodies.” Antibody screens are performed as part of routine pretransfusion testing for blood recipients, to predict compatibility between recipient antibodies and donor red blood cells. In this test, serum or plasma is added to RBCs from between two and four group O persons specifically chosen by the manufacturer to carry antigens that could be the target of significant RBC antibodies. The test can be done using one of several platforms, primarily either tubes, gel testing, or solid-phase testing. If the antibody screen is positive, in most cases the next step would be to perform antibody identification. If the screen is negative, there is a very high likelihood that no significant antibodies are present (though some rare antibodies against low-incidence RBC antigens could still be present).

Don’t let me catch you saying something silly like, “The antibody screen was negative, so there were no antibodies!” That is not correct; rather, you should say, “The antibody detection test was negative, so there were no antibodies detected!” This test is not perfect (no test can be), so it is absolutely possible for significant antibodies (especially ones targeted against rare red cell antigens) to go undetected on routine tests.

Two important things to remember about antibody screening:

  • Group O red cells are used to avoid interactions with ABO antibodies. Any incompatibility with the screen cells should be due to antibodies other than normally occurring ABO antibodies.
  • Antibody screens are done on recipients, as mentioned, but many forget the requirement that they are also performed on every blood donor! Plasma-rich products from donors with significant antibodies cannot be used, but the RBCs may be used if labeled with the antibody specificity (but many hospitals will not accept such units).

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