ABO discrepancies describe unexpected reactions in forward or reverse groupings
Serum and RBC reactions are usually very strong (3+ or 4+)
Weak reactions usually indicate an ABO discrepancy
They are due to technical errors, problems with the patients RBCs, plasma or both
ABO discrepancies can be classified into the following categories:
Group 1: problem with reverse grouping (unexpectedly weak / absent) = weakly-reacting / missing antibodies in patient’s serum
Group 2: problem with forward grouping = weak / missing antigen expression on patient’s RBCs
Group 3: problem with both forward and reverse grouping caused by protein or plasma abnormalities
e.g. rouleux
Group 4: problem with both forward and reverse grouping caused by miscellaneous problems
Cold autoantibodies causing agglutination at room temperature
Presence of two types of ABO cells in the circulating caused by ABO-incompatible SCT
All discrepancies should be resolved before blood products are issued, unless there is an emergency.If transfusion is required before resolution, group O products should be supplied.
Mixed Field Reactions
These are not ABO discrepancies, but refer to a specific reaction grade with two distinct sets of reactions
Prior transfusion (e.g. group O transfusion to non-O recipient)
ABO incompatible stem cell transplant
Large feto-maternaal haemorrhage (very rare)
A3 or B3 subtypes
Twin-twin transfusions
Technical Errors
Sample collection from the wrong patient
Labeling errors
Failure to add reagents
Failure to add sample
Using expired or contaminated reagents
Adding reagents or sample in wrong quantities
Transcription errors
Using the wrong sample
Uncalibrated centrifuge
Warming during centrifugation process
Mis-reading of strength of reaction
ABO Antigens in Disease States
Disease states can alter the expression of ABO antigens / antibodies
Diseases which can weaken antigen expression:
Acute leukaemias
Chromosome 9 translocations (ABO gene is located on chromosome 9)
Haemolytic anaemia (or any condition which causes stress haematopoiesis)
Hodgkin lymphoma
Weakened antigen expression often manifests as mixed-field agglutination (tiny agglutinates in a sea of unagglutinated cells)
Antigen expression often follows disease course (gets stronger if disease enters remission)
Diseases which can weaken antibody expression:
CLL or myeloma which can be associated with hypogammaglobulinaemia
Resolve by running protein electrophoresis or demonstrating low IgG, IgA and IgM
Lymphomas which can decrease the gamma globulin fraction
Polysaccharide of the E. coli O86 subtype (often associated with colorectal cancer)
Can cause an “acquired B” phenotype in group A individuals due to adsorption of a B-like polysaccharide from E. coli
B-line polysaccharide reacts with human source anti-B
Increase in blood group-specific soluble substances (BGSS) in the serum
Most often seen in patients with CA stomach or pancreas
ABO antigen expression remains the same
BGSS in patient’s serum can neutralise antisera used in forward grouping
Solution: suspend patient’s cells in saline instead of plasma / serum
Group 1 Discrepancies
Group 1 discrepancies are the most common
They may be seen in:
Newborns (production of ABO antibodies starts at 4-6 months of age)
Elderly (reduced production of ABO antibodies)
Hypogammaglobulinaemia
Malignancies such as CLL, myeloma, lymphoma
Immunosuppression
Post-SCT following heavy immunosuppression
Congenital agammaglobulinaemia
Plasma dilution following FFP transfusion or plasma exchange / exchange transfusion
ABO subtypes
Some A2 individuals have anti-A1. Anti-A1 is usually a cold-reacting IgM, and is of no clinical significance unless it reacts at 37°C
Para-Bombay blood groups
Presence of other allo-antibodies to high-incidence antigens reacting with reagent cells
Resolution
Confirm with history
For elderly patients / those with hypogammaglobulinaemia:
Add one or two extra drops of plasma to the reaction
Incubate at room temperature for 15-30 minutes
Incubate at 4°C for 15 minutes
Incubation at 4°C requires the use of auto-controls or control O+ cells as incubation at cold temperatures can cause agglutination due to activation of commonly-occurring cold-agglutinins such as anti-I, which react with all adult RBCs
For patients with an A2 subgroup:
Test with anti-A1 lectin: A1 patients will have a positive reaction, while A2 patients will have no reaction
Group 2 Discrepancies
Causes
ABO subgroups (e.g. A2 subgroup causing weaker reaction with anti-A1 antibodies, or weak A / B subgroups with reduced antigen expression
Weakened antigen expression in disease states (e.g. leukaemia)
Acquired B phenomenon (usually associated with colorectal cancer)
Presence of blood group-specific soluble substance (BGSS) in the plasma (associated with stomach and pancreatic cancer)
Antibodies in reagent anti-A or anti-B antisera against low-incidence antigens
Resolution
For ABO subgroups: use specific antisera (e.g. anti-A2)
For weak antigen expression:
Incubate at room temperature for 15-30 minutes
Incubate at 4°C for 15 minutes
Incubation at 4°C requires the use of auto-controls or control O+ cells as incubation at cold temperatures can cause agglutination due to activation of commonly-occurring cold-agglutinins such as anti-I, which react with all adult RBCs
For the acquired B phenomenon:
Test at pH < 6 or > 8.5. B antisera will not react with the acquired B at this pH
Reduce the reactivity of acquired B by treatment with acetic anhydride
Reactivity of normal B antigen is not affected by treatment with acetic anhydride
Do secretor studies: patients will secrete A substance, not B substance (as opposed to real group B patients, who will secrete B substance instead of A substance)
For patients with BGSS:
Wash red cells and suspend them in saline instead of plasma
For patients with low-incidence antigens which may react with antibodies in the antisera:
Change lot numbers; the new lot should not have the low-incidence antibody and thus will not non-specifically react with the red cells.
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