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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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ABO Discrepancy Resolution: General Guidelines

Unresolved ABO discrepancies can compromise patient safety. When encountered, it is critical to reach a resolution in order to report the correct patient ABO group.
Generally the ABO group of the patient can be hypothesized from the patient data with varying degrees of certainty. Deriving a hypothesis about the ABO type is necessary so that you can determine the most appropriate problem-solving steps to follow for resolution.
The following guidelines may help with ABO discrepancy resolution:
  1. ABO reactions with reagent antisera and red cells are generally strong (3 – 4+); weak reactions should be noted.
  2. Mixed field reactions are not typically expected when performing ABO forward typing.
  3. Patient history and clinical data often provide hints regarding possible resolution. Useful patient history information includes previous ABO typing results, transfusion history (number of units and ABO type of units), transplantation history, and the volume of fluids administered prior to admission.
Forward Typing
Reverse Typing
A1 Cells
B Cells

In this case, the forward typing would indicate that the patient is a group A, demonstrating strong reactions with both anti-A and anti-A,B. The reverse typing is consistent with a group A except for the weak reaction seen with A1 cells. Given the strength of this reaction (1+), it is most likely not due to anti-A. The most probable type for this patient is group A. Your next step should be gathering data that will attempt to explain and optimally eliminate the unexpected reaction with A1 cells.