W10L3 - ABO Discrepancies Flashcards
What are ABO Discrepancies
When the forward and reverse groups don’t match
Must be resolved before issue of blood product
- if RBC unit(s) are required before resolution, report the ABO group as Indeterminate and issue group O cells
Strength of reactions might give you a clue to the cause
- forward grouping reactions are usually 4+
- reverse grouping reactions are usually 3+ to 4+
- weaker reactions indicate the source of the problem
Causes of ABO Discrepancies
Most common cause is clerical or technical error
Clerical error
- incorrect sample collection/labelling
- incorrect/insufficient labelling of tubes/cards
- incorrect recording of results
Technical error
- fibrin formation in sample
- sample mix-up during setup
- failure to add reagents
- addition of incorrect reagent (i.e. wrong cells)
- contaminated reagents
- incorrect cell concentration / centrifugation / reaction temperature / reading
technique
Resolution = re-test sample, collect new sample
Group 1 Discrepancies
Unexpected reactions in the reverse group due to weakly reacting or missing aby’s
Example of results:
Anti-A: 4+
Anti-B: 0
A cells: 0
B cells: 1+
Individuals with depressed antibody production
Dilution of existing antibodies by transfusion of large volumes of plasma
Resolution
- no need to perform reverse grouping on newborns
- add more plasma then re-centrifuge
- requires auto control and O cell control (cells vs patient plasma)
Group 2 Discrepancies
Unexpected reactions in the forward group due to missing or weakly
reacting antigens
Least encountered
ABO subgroups
Group 2 Discrepancies - Depressed Antigen Production
Due to:
- leukaemia and Hodgkin’s lymphoma
- A or B antigen expression may be decreased
Example of results:
Anti-A: 0
Anti-B: 1+
A cells: 4+
B cells: 0
Resolution:
- incubate reactions @ RT for 15-30 minutes before centrifugation
- incubate reactions @ 4°C for 15-30 minutes before centrifugation
Group 2 Discrepancies - Excess Production of Soluble A/B
A.k.a Blood Group Specific Soluble Substance (BGSSS)
Associated w/ stomach and pancreatic Ca
Present in the suspension of unwashed RBCs
The BGSSS neutralises anti-A or anti-B grouping reagents
Presents as weakened reaction in forward grouping reaction
Resolution:
- wash cells with saline then re-test
Group 2 Discrepancies - B(A) Phenotype
Found in ~1% of group B donors
Individuals produce high concentrations of B glycosyltransferase that catalyses the addition of D-galactose AND N-acetyl-D-galactosamine
Mostly B antigen, with weak expression of A antigen, on RBCs
Produce an anti-A antibody that agglutinates A1 and A2 RBCs
Example of results:
Anti-A: 1+
Anti-B: 4+
A cells: 4+
B cells: 0
Only detected when the MHO4 anti-A monoclonal antibody is used for forward grouping reactions
Solution:
- use a different grouping reagent
Group 2 Discrepancies - Acquired B
Group A individuals with gut diseases (Colon Ca, septicaemia) Bacterial deacetylases remove acetyl group from GalNAc (N-acetylgalactosamine) Some anti-B reagents bind to D-galactosamine → w+ rxn Example of results: Anti-A: 3+ Anti-B: 1+ A cells: 0 B cells: 4+ Not a true B antigen Solution: - use a different anti-B reagent - ↓ pH
Group 3 Discrepancies
Due to protein or plasma abnormalities → rouleaux Conditions: - multiple myeloma - Waldenstrom’s macroglobulinemia - ↑ [Fbg] - Wharton’s Jelly Rarely affects testing performed in CAT Example of results: Anti-A: 4+ Anti-B: 1+ A cells: 1+ B cells: 4+ Resolution: - look at cells under microscope for rouleaux formation - wash cells with saline - perform a saline replacement
Group 4 Discrepancies - Recipient of Out-of-Group RBC Transfusion
E.g. group A recipient transfused w/ group O RBC, for instance, in an emergency situation
RBCs in patient blood are a mix of group A and group O
- mixed field agglutination in forward group
Will group as A in reverse group
Recipients of large volumes of RBCs may have their RBCs completely replaced by donor cells
Resolution:
- patient history; revert patient to group-specific units ASAP
Group 4 Discrepancies - Recipient of additional ABO antibodies
Example of results:
Anti-A: 4+
Anti-B: 0
A cells: 1+
B cells: 4+
Recent transfusion of out-of-group, plasma containing blood components (i.e. platelets)
Administration of intravenous immunoglobulin (IVIg)
Resolution:
- patient history; if transfusion is required, issue Gp O RBCs
- low titre anti-A/B products are available, which may be used for future transfusions
Group 4 Discrepancies - Patient Produces a Cold Reacting Alloantibody Reactive at RT
i.e. Anti-M, anti-P1, anti-Lea
Antibody binds to antigens on reagent A1 and/or B cells
Resolution:
- perform antibody screen/ID at RT to identify antibody
- phenotype A1 and B cells to identify cells negative for the corresponding Ag
- use Ag negative cells for reverse grouping
Group 4 Discrepancies - Patient Produces an Anti-Reagent Antibody
Produces an antibody possibly towards: - dyes in Anti-A or Anti-B - preservatives in reagent antibodies - preservatives in reagent RBC preps Solution: - wash patient / reagent cells and resuspend in saline
Group 4 Discrepancies - cisAB
Remember, an offspring’s ABO group is determined by their parents
Usually a single maternal and paternal allele is inherited
In cisAB individuals, a single allele expressing both A AND B glycosyltransferases are inherited from an AB parent, and a single allele (usually O) from the other parent
cisAB individuals have decreased glycosyltransferase production => ↓ ag expression => weak forward reactions
Usually also produce a weak anti-B antibody
- reacts with B cells (and ? normal AB cells) but not cisAB cells
Example of results:
Anti-A: 2+
Anti-B: 2+
A cells: 0
B cells: 1+
Resolving ABO Discrepancies
Clerical checks, re-test sample Wash patient/reagent cells, re-test Check patient history - age - disease state - transfusion (cells, plasma products/platelets/IVIg) Determine whether the discrepancy is in the forward or reverse group (reaction strength) Know your reagents Begin testing for specific causes
