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ABO Discrepancies

QuestionAnswer
Antigen present on RBCs > matching antibody absent in plasma. Antigen absent on RBCs > antibody is present Landsteiner’s Rule.
What does forward grouping test? Patient RBC antigens, using known anti-A and anti-B reagent
What does reverse grouping test? Patient serum antibodies, using known A1 and B reagent cells
List the expected reactions for anti-A, anti-B, A1 and B: group A + , 0 , 0 , +
List the expected reactions for anti-A, anti-B, A1 and B: group B 0 , + , + , 0
List the expected reactions for anti-A, anti-B, A1 and B: group AB + , + , 0 , 0
List the expected reactions for anti-A, anti-B, A1 and B: group O 0 , 0 , + , +
Donor RBCs must lack antigens that recipient's plasma has antibodies against RBC compatibility rule
Donor plasma antibodies must not attach the recipient's RBC antigens Plasma compatibility rule
universal RBC donor O negative: lacks A, B and D antigens.
universal RBC recipient AB positive: no anti-A, anti-B or anti-D.
Universal plasma donor? Group AB: contains no anti-A or anti-B.
Compatible plasma for a group A patient? A or AB.
Compatible plasma for a group O patient? O, A, B or AB (O is the universal plasma recipient).
Compatible RBCs for a group B patient? B or O.
Risk of giving D+ RBCs to a D-negative patient? Anti-D formation: future transfusion reactions and HDFN in later pregnancies.
Three pre-transfusion tests? ABO/Rh typing, antibody screen, crossmatch.
Define ABO discrepancy. Forward and reverse groupings disagree, or reactions differ from what is expected for the group.
Can you report the ABO group with an unresolved discrepancy? No. Record the results, delay interpretation until resolved.
First step in investigating a discrepancy? Rule out technical/clerical error and repeat testing.
Order of investigation? Technical errors → patient history → type-specific enhancement.
Which reaction is usually the one in doubt? The weakest reaction.
Type I discrepancy affects what? Reverse grouping (serum). Most common type.
Type II discrepancy affects what? Forward grouping (cells). Least common type.
Type III discrepancy? Both forward and reverse: protein/plasma abnormalities (rouleaux, plasma expanders, Wharton’s jelly).
Type IV discrepancy? Miscellaneous: cold autoagglutinins and unexpected alloantibodies.
Causes of weak or missing reverse reactions? Newborn or elderly, hypogammaglobulinemia (CLL, lymphoma), immunosuppression, dilution (plasma exchange, transfusion).
How to enhance weak reverse reactions? Room temp 15–30 min, then 4°C 15–30 min, with autocontrol and O cell controls.
Group A patient’s serum reacts 1+ with A1 cells. Likely cause? A2 (or A2B) with anti-A1; confirm with anti-A1 lectin and A2 cells.
Source of anti-A1 lectin? Dolichos biflorus.
Source of anti-H lectin? Ulex europaeus.
Bacterial (E. coli) deacetylase converts A sugar N-acetylgalactosamine to galactosamine, resembling the B sugar. Acquired B mechanism?
Typical history in acquired B? GI disease: colon/bowel carcinoma or bowel obstruction. Serum still has anti-B.
Causes of a mixed-field forward reaction? Recent non-identical transfusion, bone marrow transplant, or chimera.
Causes of a mixed-field forward reaction? Recent non-identical transfusion, bone marrow transplant, or chimera.
Causes of rouleaux? Multiple myeloma, Waldenström’s macroglobulinemia, hypergammaglobulinemia, plasma expanders.
How do you resolve rouleaux? Saline replacement: washing away excess protein disperses pseudoagglutination; true agglutination remains.
Signs of a potent cold autoagglutinin and its fix? All cells, including autocontrol, react at immediate spin. Prewarm technique or warm-saline-washed cells.
Cold antibodies that can react with reagent cells in reverse typing? Anti-M, anti-N, anti-I, anti-P1. Review the antibody screen.
Effect of incompletely clotted serum? Fibrin traps RBCs and mimics agglutination (extra reverse reaction).
Transfusion needed before the discrepancy is resolved? Group O RBCs and group AB plasma.
Created by: MOrfCLS
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