ABO DiscrepanciesDr. MH Saiemaldahr Blood Bank

drmsaiem

ABO AntibodiesGenerally IgM class antibodiesFor Group A and Group B persons the predominant antibody class is IgMFor Group O people the dominant antibody class is IgG (with some IgM)React best at room temperature (22-24oC) or below in vitro.Activates complement to completion at 37oC Can cause acute Hemolytic Transfusion reactionsRBC Immune form: Predominantly IgG

drmsaiem

ABO AntibodiesTime of appearance:Generally present within first 4-6 months of lifeReach adult level at 5-10 years of ageLevel off through adult lifeBegin to decrease in later years: >65 years of age

drmsaiem

A and B SubgroupThey both react strongly with reagent anti-A. 80% of group A individuals phenotype as A1 20% phenotype as A2

Reagent anti-A is a mixture of two Abs ;

anti-A which react with both A1 and A2 cells.anti-A1 which reacts with A cells but not with A2 cells in simple testing .

drmsaiem

A and B SubgroupQualitative difference due to ;

1-8 % of A2 and 22-35 % of A2B individuals produce a readily identifiable anti-A1 in their serum.

Quantitative differenceA2 cells carry 25 % as many A antigen sites as do A1 cells A1 individuals make A antigen from all type II chains ( H1-4 ) .A2 individuals produce A antigen only from H1 and H2 precursors.

drmsaiem

A and B SubgroupDifferentiation between the A blood subgroupsReagent anti-A is a mixture of two AbsThe two Abs can be functionally separated by adsorption with A2 cells.

Anti-A1-lectin: is another source of anti-A1. lectins are seed extracts that agglutinate human cells with some degree of specificity. The seeds of the plant Dolichos biflorus serve as the source of the anti-A1 lectin this reagent agglutinate A1 or A1B cells but does not agglutinate A2 or A2B cells.

drmsaiem

A and B SubgroupOther A subgroups: RBC of the A int, A3, Ax, Ay or A cl. are only rarely seen in transfusion practice.

Subgroup of B: infrequent than the weaker subgroup of A, identified by anti-B and anti-A,B. Subgroups B3 , Bx , Bm and Bcl .

drmsaiem

ABO DiscrepanciesABO discrepancies happen when there is no match in results between forward and reverse grouping.

ABO discrepancies are usually technical in nature and can be simply resolved by correctly reporting the testing and carefully checking reagents with meticulous reading and recording of results.

drmsaiem

ABO DiscrepanciesThere are some ABO discrepancies that can happen due to technical errors and may lead to false positive or false negative reactions.

False positive reactions are due to;Un-calibrated centrifugesContaminated reagentsDirty tubes or glassware

drmsaiem

ABO DiscrepanciesFalse negative reactions can be due to many causes

Failure to add serum or reagentsUse of incorrect reagents or samplesCell suspension is too heavy or too lightInadequate identification of samples or test tubes

drmsaiem

ABO DiscrepanciesGroup I discrepancies These discrepancies are between forward and reverse grouping due to weak reaction or missing antibodies.

These kind of discrepancies are the most common.

The reason for the missing antibody or weak reaction is that the patient has depressed antibody production or cannot produce the ABO antibodies.

drmsaiem

ABO Discrepancies This type of discrepancy can be seen in new born infants, elderly patients.

Patients with lymphoma.

Patients using immunosuppressive drugs.

Patients with immunodeficiency disease, BM transplant.

drmsaiem

ABO DiscrepanciesResolving discrepancies

Eliminate all technical errorsEnhancing the reaction in reverse groupingIncubate the patients serum with reagent cells at room temp. for 15 mins.

drmsaiem

ABO DiscrepanciesGroup II discrepancies These discrepancies are between forward and reverse grouping due to weak reaction or missing antigens. This group is the least one. Can be caused by some subgroups of A or subgroups of B or both. Also it can be present in patients with leukaemia and hodgkins disease.

To resolve the problem wash the patients cells with saline.

drmsaiem

ABO DiscrepanciesGroup III discrepancies

These discrepancies are between forward and reverse grouping due to protein or plasma abnormalities.

These can be caused by elevated levels of globulin from certain diseases such as multiple myloma, hodgekins lymphoma. Some are caused by (Rouleaux formation).

drmsaiem

ABO DiscrepanciesRouleaux or red cells result from a stacking of erythrocytes that adhere in a coin-link fashion giving the appearance of agglutination.

To resolve this kind of problem, washing the patients red cells with saline or adding a drop or two of saline to the tube in case of rouleaux formation.

If the agglutination is true red cell clumping will remain.

Cord blood must be washed 6-8 times in forward grouping ONLY.

drmsaiem

ABO DiscrepanciesGroup IV discrepanciesThese kind of discrepancies are between forward and reverse groping due to miscellaneous problems.

Polyagglutination can occur due to exposure of hidden erythrocyte Ag. (T antigen) in patients with bacterial or viral infection.

Bacterial contamination in vitro or vivo produces an enzyme that alters and exposes the hidden Ag. on red cell leading to T activation.

drmsaiem

ABO DiscrepanciesSome examples of discrepancies

Example 1Forward grouping: anti-A =O, anti-B =O, anti-AB= OReverse grouping: A1 cells= O, B cells =OBlood group: OPossible discrepancy: Missing Ab. Or group I discrepancy

drmsaiem

ABO DiscrepanciesExample 2

Forward grouping: anti-A = 4+,anti-B =O, anti-AB =4+Reverse grouping: A1 cells =1+, B cells =4+Blood group: APossible discrepancy: Missing Ag. Or group II discrepancy

drmsaiem

ABO DiscrepanciesExample 3

Forward grouping: anti-A 4+,anti-B 2+,anti-AB 4+Reverse grouping: A1 cells 4+, B cells 4+Blood group : APossible discrepancy

Rouleaux formation

drmsaiem