ABO Subgroups and Discrepancies

Nada Jamjoom

Faculty of Applied Medical Sciences

BLOOD BANK

MEDICAL TECHNOLOGY

KAU

ABH Antigens

H antigen

ABO Antibodies

• ABO Abs are generally IgM class antibodies.

• For Group A and Group B individuals the predominant antibody class is IgM.

• Serum from Group O individuals contains not only anti-A and anti-B but also anti-A,B.

• Anti-A,B is a mixture of class IgG and IgM.

• The anti-A,B “immune” antibodies are predominantly IgG.

ABO Antibodies

Time of appearance:

•Generally present within first 4-6 months of life

•Reach adult level at 5-10 years of age Level off through adult life

•Begin to decrease in later years: >65 years of age

ABO Subgroups• Von Dungern in1911 described 2 different A Ag based on reactions between group A

RBCs and anti-A and anti-A1 antisera.

• Group A red cells that react with both anti-A & anti-A1 are classified as A1.

• Group A red cells that react with anti-A and not anti-A1 are classified as A2.

• The majority (80%) of the A and AB population are A1 or A1B; the remaining 20% are A2 or A2B.

• The production of both types of antigens (A1 and A2) is a result of an inherited gene at the ABO locus & the immunodominant sugar on both A1 and A2 RBCs is N-acetyl-D-galactosamine.

Difference between A1 and A2

• The difference between A1 and A2 is both quantitative and qualitative.

Quantitative difference

• Inheritance of an A1 gene elicits production of high concentrations of the enzyme α-3-N-acetylgalactosaminyltranferase, which converts almost all of the H precursor structure to A1 antigens on the red cells.

• The number of A1 antigen sites is higher than the number of A2 antigens sites on the red cell because A1 gene is a very potent gene that creates large numbers of A1 antigens sites on RBC.

Difference between A1 and A2

Qualitative differences

•1 to 8% of A2 individuals produce anti-A1 in their serum

•25% of A2B individuals produce anti-A1.

Difference between A1 and 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 .

• The seeds of the plant Dolichos biflorus serve as a source of anti-A1 which is known as anti-A1 lectin.

• This reagent agglutinates A1 or A1B but does not agglutinate A2 or A2B cells.

A1 versus A2 Phenotype

Reactions of patient’s red cells with

Blood Group Anti-A (from B Sera) Anti-A1 Lectin

A1 + +

A2 + Negative

A1 has 2 antigens A and A1

A2 has only one, A antigen

Weak A and B Subgroups

• Other A subgroups: RBC of the A end, A3, Ax, Ay or A el. 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 Bel .

ABO Discrepancies

• A discrepancy occurs when the red cell testing does NOT match the serum testing results

• In other words, the forward does NOT match the reverse

• 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.

ABO Discrepancies

• Most of the time, the problem is technical– Mislabeled tube– Failure to add reagent– Either repeat test on same sample, request a new

sample, or wash cells

• Other times, there is a real discrepancy due to problems with the patient’s red cells or serum.

Technical Errors

• Clerical errors– Mislabeled tubes– Patient misidentification– Inaccurate interpretations recorded– Transcription error– Computer entry error

• Reagent or equipment problems– Using expired reagents– Using an uncalibrated centrifuge– Contaminated or hemolyzed reagents– Incorrect storage temperatures

• Procedural errors– Reagents not added– Manufacturer’s directions not followed– RBC suspensions incorrect concentration– Cell buttons not resuspended before grading agglutination

ABO Discrepancies

Group I Discrepancies

• Group I discrepancies are between forward and reverse groupings because of weekly reacting or missing antibodies.

• Group I discrepancies are the most common type. • If a reaction in the reverse grouping is weak or missing

Group I discrepancy.• It means that the patient has depressed antibody

production or cannot produce the ABO antibodies.

ABO Discrepancies

Examples of Group I Discrepancies

• Newborns Do not form antibodies until they 3-6 months • Elderly patients Weakened antibody activity

• CLL, malignant lymphoma, using immunosuppressive drugs can cause hypogammaglobulinemia (little or no antibody production)

ABO Discrepancies

Resolution of Group I Discrepancies

• Eliminate all technical errors

• Determine patients age, diagnosis

• Incubate patient’s serum with reagent A1 and B cells for 15 to 30 minutes (RT) to enhance antibody reactions

• If negative, place serum-cell mixture at 4°C for 15 to 30 minutes

ABO Discrepancies

Group II Discrepancies

• These discrepancies are between forward and reverse groupings because of weakly reacting or missing antigens.

• Group II discrepancies is the least common type.

ABO Discrepancies

Examples of Group II Discrepancies

• Subgroups of A and or subgroups of B may be present.

• Leukemias may yield weakened A or B antigens.

• Hodgkin’s disease

• “Acquired B” phenomenon is most often associated with lower GI tract disease– Cancer of colon/rectum– Intestinal obstruction– Gram negative septicemia (i.e. E. coli)

ABO Discrepancies

Acquired B

• Bacteria (E. coli) have a deacetylating enzyme that modify the immunodominant BG A sugar….

Group A individual

N-acetyl galactosamine

Acquired B

Phenotype

Bacterial enzyme removes acetyl group

Galactosamine now resembles

D-galactose (found in Group B)

ABO Discrepancies

Resolution of Group II Discrepancies

ABO Discrepancies

• Eliminate all technical errors

• Wash patient’s cells with saline

• The reaction can be enhanced by incubating the test mixture at RT for up to 30 minutes to increase the association of Ab with Ag.

• If negative, reduce the temperature to 4°C.

• Testing the patient’s serum against autologous RBCs gives a negative reaction because the anti-B in the serum does not agglutinate autologous RBCs with the acquired B Ag.

ABO Discrepancies

• These discrepancies are between forward and reverse grouping due to protein or plasma abnormalities and result in Rouleaux formation.

• These can be caused by elevated levels of globulin from certain diseases such as multiple myeloma and Hodgekin’s lymphoma.

• Wharton’s jelly ( a viscous mucopolysaccharide material present on cord bloods).

Group III Discrepancies

ABO Discrepancies

• Rouleaux 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 patient’s 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.

Resolution of Group III Discrepancies

ABO Discrepancies

• These 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.

• This problem can be resolved by using monoclonal antibody typing reagent.

Group IV discrepancies

Common sources of technical errors resulting in ABO discrepancies

False Negative False Positive Over centrifugation and over reading

Use of incorrect reagents or samples

Failure to add serum or reagents

Cell suspention is too heavy or too light

Inadequate identification of samples or test

tubes

Contaminated reagents

Dirty tubes or glassware

ABO Discrepancies

Example I

Forward Grouping

Reaction of Patient’s Cells with

Reverse Grouping Reaction Patient’s

Serum with

Anti-A Anti-B A1 cells B cells

Patient Negative +++ Negative Negative

Possible discrepancy: Group I discrepancy; because of weakly reacting or missing antibodies.

Patient’s probable group: B

ABO Discrepancies

Forward Grouping

Reaction of Patient’s Cells with

Reverse Grouping Reaction Patient’s

Serum with

Anti-A Anti-B A1 cells B cells

Patient ++++ ++ ++ ++++

Example II

Possible discrepancy: Group III discrepancy; caused by Rouleaux formation

Patient’s probable group: A

ABO Discrepancies

Example III

Forward Grouping

Reaction of Patient’s Cells with

Reverse Grouping Reaction Patient’s

Serum with

Anti-A Anti-B A1 cells B cells

Patient ++++ negative ++ ++++

Possible discrepancy: Group II discrepancy; because of weakly reacting or missing antigens

Patient’s probable group: A (subgroup A2)

ABO Discrepancies

Example IV

Forward Grouping

Reaction of Patient’s Cells with

Reverse Grouping Reaction Patient’s

Serum with

Anti-A Anti-B A1 cells B cells

Patient ++++ ++ Negative ++++

Possible discrepancy: Group II discrepancy; caused by an acquired B Ag

Patient’s probable group: A

ABO Discrepancies

Example V

Forward Grouping

Reaction of Patient’s Cells with

Reverse Grouping Reaction Patient’s

Serum with

Anti-A Anti-B A1 cells B cells

Patient ++ + ++++ ++++

Possible discrepancy: Group IV discrepancy; caused by T activation.

Patient’s probable group: O

ABO Discrepancies