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    RBC Units to Screen for Compatibility

    Estimates number of donor RBC units to screen to obtain a desired number of antigen-negative units.
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    When to Use
    Why Use
    • Use in blood bank setting to ensure recipient compatibility with RBCs for transfusion.
    • The calculator is typically used for patients with one or more alloantibodies, or for patients at risk for development of alloantibodies. Blood bank laboratory staff may find this calculator particularly useful.

    An accurate estimate of the number of RBC units to screen helps in the management of blood bank workflow. A prohibitively large estimate of the number of units to screen may require contact outside of the patient’s blood bank (i.e., regional blood donor center, rare blood unit registry).

    Antigen profile: should the screen exclude RBC units with this antigen?
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    Result:

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    Next Steps
    Evidence

    Advice

    • Follow AABB Standards for respective compatibility testing steps.
    • The default values provided are for a Caucasian donor population. They can be replaced with antigen frequencies in non-Caucasian donor populations (or antigen frequencies for antigens not explicitly listed).

    Formula

    x = number of units required / frequency of units negative for the antigen

    where x = minimum number of units to antigen type

    Example for patients with single antibodies:

    • Four c-negative donors are required for a patient with anti-c.
    • The frequency of the c antigen is 80%. 
    • x = 4 / (1 - 0.8) = 20
    • Answer: a minimum of 20 donors should be antigen typed.
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