ABO & Rh Discrepancies

ABO & Rh Discrepancies

M. Zaharna Blood Bank 2009

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

Definition


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 resolved

In RECIPIENTS 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 DONORS the discrepancies must be resolved before any blood is labeled with a blood type.


Categories of ABO Discrepancies

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

ReactionsD. Serum Typing- Missing Reactions


A- Cell Typing: Additional Reactions


1- Polyagglutinable 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+


2- Acquired 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


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)


3- Non-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 anit-B yet.


3- Non-specific Agglutination 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 X'S before determining the type of the baby, or request new sample from heel


4- Sensitized 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 Reactions


1- Subgroups

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-A1, anti-H & anti-A,B


0 0 0 4+


2- Altered Antigen Expression

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


0 0 0 4+


3- Chimera

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)


4- Excessive 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 Reactions


1- Alloantibodies Abs other than anti-A or -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


2- Autoantibodies

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


3- Rouleaux 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


4+ 0 2+ 4+


D- Serum Typing Missing Reactions


1- Newborns

Infants develop ABO Abs by 3-6 months of age

Serum typing before this time: Weak reaction Negative reaction


2- Patients with Hypogamma- globulinemia

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


3- Chimera 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


4- Reagent Problems Deterioration of Ags on A or B cells used

for serum typing Weak Or negative reaction


Rh 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 reactions

1. Positive direct antiglobulin test2. Polagglutinable red cells3. Cold agglutinins or Rouleaux formation


1- Positive 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


2- Polagglutinable 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


3- Cold 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

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ABO & Rh Discrepancies

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