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The page below is a sample from the LabCE course ABO Typing Discrepancies. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Reverse Typing Discrepancies: Identify the Unexpected Antibody

Cold reacting antibodies (<37°C) can interfere with reverse ABO typing. For example, anti-M is notorious for generating reverse typing discrepancies due to the high prevalence of the M antigen on reagent red blood cells and the nature of testing reverse grouping at room temperature. This discrepancy is particularly found in A, B, and AB patients, as the reverse typing of these samples should normally demonstrate negativity in one or both of the reagent red blood cells.
In order to resolve a reverse ABO discrepancy that is suspected to be caused by an alloantibody or autoantibody, there are a few things that need to be completed prior to resolution:
  1. Complete an antibody screen and antibody identification panel, if needed. Knowing the class of alloantibody present will indicate if that particular antibody is causing the discrepancy.
  2. Pre-warming of the reverse ABO typing. Pre-warming techniques prevent colder reacting antibodies from forming immune complexes with their corresponding antigens.
    1. Patient plasma and reagent red blood cells should be warmed separately at 37°C for about 15 minutes.
    2. After pre-warming, reverse ABO testing should be conducted as normal.
    3. Results should be immediately read and reported.

Successful pre-warming technique will result in the elimination of alloantibody and autoantibody interference.