ABO & Rh DiscrepanciesABO & Rh Discrepancies

When the results of the forward grouping (patient cells) do not correspond to the results of the reverse grouping (patient serum) or abnormal reactivity is present (i.e. Mixed Field)

i.e. the forward does NOT match the reverse

DefinitionDefinition

Patient Anti-A Anti-B A-Cells B-Cells

A 4+ 1+ 0 4+

B 0 4+ 1+ 0

C 4+ 4+ 1+ 0

D 0 3+ 0 0

Patient A: Additional reaction with anti-B and patients cells.

Patient B: Weak reaction with patients serum and A-cells.

Patient C: Additional reaction with patients serum and A-cells.

Patient D: Missing reactions with patients serum A-cells

ABO Discrepancies must be resolvedABO Discrepancies must be resolved

In RECIPIENTSRECIPIENTS the discrepancies must be resolved

before any blood component is transfused. – If not resolved before blood is needed, transfuse Group O

(O NEGATIVE if there is a discrepancy in the Rh type

also).

In DONORSDONORS the discrepancies must be resolved before

any blood is labeled with a blood type.

Categories of ABO DiscrepanciesCategories of ABO Discrepancies

A. Cell Typing – Additional ReactionsB. Cell Typing – Missing ReactionsC. Serum Typing- Additional ReactionsD. Serum Typing- Missing Reactions

A- Cell Typing: Additional ReactionsA- Cell Typing: Additional Reactions

11 - -Polyagglutinable Red CellsPolyagglutinable Red Cells

The removal of red cell N-Acetyl neuraminic acid by bacterial enzymes expose the T-Ag on the cell membrane.

Antibodies to T-antigens are naturally present in most human sera.

This Ab can also be found as a contaminant in some ABO typing reagents.

This cause unexpected agglutination of T Ags on red cells.

ANTI-A ANTI-B A CELL B CELL

4+ 4+ 0 4+

22 - -Acquired AntigensAcquired Antigens

• Microbial deacetylating enzymes such as E. coli cleave off the N-Acetyl of the Group A N-acetyl-galactosamine

• The remaining galactosamine becomes similar to the Group B galactose

• Anti-B react with this B-like Ag causing agglutination

• A-like Ag can also be acquired

ANTI-A ANTI-B A CELL B CELL

4+ 2+ 0 4+

Group A individual

N-acetyl galactosamine

Acquired B

Phenotype

Bacterial enzyme removes acetyl group

Galactosamine now resembles

D-galactose (found in Group B)

33 - -Non-specific AgglutinationNon-specific Agglutination

Wharton’s Jelly – gelatinous substance derived from connective tissue that is found in cord blood and may cause false agglutination

Wharton’s Jelly Coats newborn cord cells and the child's type may appear AB. 

We do not do a reverse on newborn blood since they have not made any anti-A or anti-B yet.

If the baby types as an AB  recheck by washing cells several times and re-testing since you need to make sure you have removed the Wharton's Jelly and the baby is truly an AB. 

Better ALWAYS wash cord blood at least 4 to 5 before determining the type of the baby, or request new sample from heel

44 - -Sensitized Red Blood CellsSensitized Red Blood Cells

Albumin in the ABO typing reagent can reduce the zeta potential

Effectively decreases the distance between red cells.

If the red cells are coated with antibody, false positive agglutination can occur

B- Cell Typing Missing ReactionsB- Cell Typing Missing Reactions

11 - -SubgroupsSubgroups

Weak variants of both A & B Carry poorly expressed Ags May not produce expected reactions with anti-A &

anti-B They are categorized according to the strength and

pattern of reaction with anti-A, anti-H & anti-A,B

ANTI-A ANTI-B A CELL B CELL

0 0 0 4+

22 - -Altered Antigen ExpressionAltered Antigen Expression

• Weak Ags may be found on RBCs of some people with diseases (Leukemia)

ANTI-A ANTI-B A CELL B CELL

0 0 0 4+

33 - -ChimeraChimera

Chimera: Two cell populations– Natural Chimera:

In utero exchange of erythropoetic tissue between non-identical twins

Strength of reaction with ABO typing depends on the percentage of A or B cells in blood

– Temporary Chimera: following blood transfusion of ABO compatible,

but not identical blood ( A received O cells)

44 - -Excessive amounts of group specific substancesExcessive amounts of group specific substances

Patients with certain types of cancer Large amounts of soluble A or B Ags Inhibit anti-A or anti-B typing reagent Can be resolved by washing RBCs prior to ABO

typing

C- Serum Typing Additional ReactionsC- Serum Typing Additional Reactions

11 - -AlloantibodiesAlloantibodies

Abs other than anti-A or anti-B Can agglutinate A or B cells if express specific

Ag Abs commonly cause this discrepancy anti-M, -N,

-S, -Lea, Leb, -P1, A1

Can be identified by testing serum with a panel of O cells that have been phenotyped for these Ags

22 - -AutoantibodiesAutoantibodies

IgM autoantibodies can cause false-positive results in cell & serum grouping

Problem can be solved by washing cells with warm saline prior to testing

In serum typing, autoabsorption can be performed Or serum typing at 37oC

33 - -Rouleaux formationRouleaux formation

Rouleaux may also give false positive cell typing if strong enough Looks like agglutination macroscopically This phenomenon is due to alteration in serum protein

concentration caused by: – elevated levels of gammaglobulins – elevated levels of fibrinogen– Also seen with plasma expanders (dextran)

Cell grouping- can be avoided by washing RBCs Serum grouping- addition of saline

ANTI-A ANTI-B A CELL B CELL

4+ 0 2+ 4+

D- Serum Typing Missing ReactionsD- Serum Typing Missing Reactions

11 - -NewbornsNewborns

Infants develop ABO Abs by 3-6 months of age Serum typing before this time:

– Weak reaction– Negative reaction

22 - -Patients with Hypogamma-globulinemiaPatients with Hypogamma-globulinemia

Have low levels of immunoglobulins Anti-A & anti-B may not be detected

33 - -ChimeraChimera

Twins that have chimeric blood group can lack A & B Abs

Chimera with 98% O cells & 2% B cells – Group as O – Serum contain only anti-A

44 - -Reagent ProblemsReagent Problems

Deterioration of Ags on A or B cells used for serum typing– Weak– Negative reaction

Rh DiscrepanciesRh Discrepancies

Rh –ve persons mistyped, & transfused with Rh +ve blood have 70% chance of becoming immunized

False +ve reactions can be identified by testing an Rh control with the patient’s red cells each time an Rh typing is performed

The test is not valid if the control causes agglutination

Causes of false positive reactionsCauses of false positive reactions

1. Positive direct antiglobulin test

2. Polagglutinable red cells

3. Cold agglutinins or Rouleaux formation

11 - -Positive direct antiglobulin testPositive direct antiglobulin test

The presence of Ab on patient’s red cells can cause a false +ve reaction with slide and tube anti-D

High protein medium reduces zeta potential allowing red cells to move closer

The cell bound Ab can cross link cells and cause agglutination

22 - -Polagglutinable red cellsPolagglutinable red cells

Rh –ve red cells that are polyagglutinable due to T or Tn activation

Agglutination occurs if anti-T or anti-Tn present in the anti-D reagent

Most anti-D reagents do not contain these antibodies

33 - -Cold agglutinins or Rouleaux formationCold agglutinins or Rouleaux formation

Rh typing is performed using serum suspended red cells

If individual’s serum contains cold agglutinin or abnormal protein, false positive reactions can occur