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 the presence or absence of “unexpected (non-ABO) antibodies.” You can think of it as an initial test designed to predict whether the patient has antibodies that could be incompatible with donor red blood cells. It’s generally a “yes/no” proposition, meaning that it’s primarily designed to answer this question: Are there any antibodies in this person’s serum/plasma that could cause a problem when the person’s serum/plasma is mixed with someone else’s red blood cells? If the antibody screen is negative, that strongly suggests that the person can receive blood from someone else without further matching (other than ABO and RhD, of course!).

Antibody screens are performed as part of routine pretransfusion testing for blood recipients. 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).

Important Caveat: Don’t let me catch you saying something silly like, “The antibody screen is negative, so there are no antibodies!” That is not correct; rather, you should say, “The antibody detection test is negative, so no antibodies are 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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