Example: Weak/Missing Reaction in the Forward Typing

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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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Example: Weak/Missing Reaction in the Forward Typing

Table 14. Example of Forward Typing Discrepancy.
Anti-AAnti-BA1 cellsB cells
Patient Results1+ MF*004+
*MF= mixed field
Most Probable ABO Type: Group A
Possible Causes: Weak subgroup of A, notably A3. Weak results with mixed field reaction in the forward grouping could also be due to the transfusion of large quantities of O red blood cells into a group A recipient, chimerism, or a group A patient transplanted with group O stem cells.
Some Strategies for Resolution: Obtain patient history, including previous ABO typing results and transfusion history. Antigen expression may be weakly expressed on red cells of persons with leukemia or other malignancies. Extended room temperature incubation of patient cells and reagent anti-sera can help to increase the reaction strength.