Haematology Watch

Haematology Watch, Vol 3, Issue 2.

LABORATORY HAEMATOLOGY


Discrepancies in blood grouping for ABH system

Mehmood


Definition:

A state of mismatch between forward (cell) and reverse (serum) ABH blood grouping test results.

 

Types:

      1.     False:

      Due to technical/clerical errors:

i.        Mislabelling of blood samples

ii.       Failure to add sample in reaction tube

iii.      Failure to add reagent in reaction tube

iv.      Expired reagent

v.       Failure to enter result

vi.      Using dirty glass ware

vii.     Poor quality control

viii.    Uncalibrated centrifuge

ix.      Over-/Under-centrifugation

x.       Failure to detect proper grade of agglutination

xi.      Failure to detach button from tube

xii.     Failure to observe haemolysis

xiii.    Contaminated reagents

xiv.   Warming during centrifugation

xv.    Making cell suspension too light or too heavy

xvi.   Delaying each step in procedure

xvii.  Delay in reading results

 

       2.     True:

Due to patient factors.

 

Presentation:

      A.    Homogenous reduced/missing agglutination when it is expected

      B.    Homogenous increased/extra agglutination when it is not expected

      C.    Mixed-field agglutination (after O blood group transfusion, Chimerism, Mosaicism, Bone Marrow transplant,

           Exchange transfusion, Foeto-maternal bleeding).

                [Note: 1. The weaker reaction is the one to be misleading! Consider stronger reactions as true ones.

                 2. Therefore, it is very important to detect properly the strength of agglutination]

 

CLASSIFICATION:

1.     Group I Discrepancies:

           - This occurs when an expected antibody is missing or weak (in reverse grouping).

           - Most common among ABH discrepancies.

           - Causes:

               New born

               Old age

               Immunosuppression (Chemotherapy, Stem cell transplant)

               Hypogammaglobulinemia (e.g. CLL)

               Agammaglobulinemia

 

2.     Group II Discrepancies:

-This occurs when an expected antigen is missing or weak (in forward grouping), or extra antigen is found.

             - Causes:

                    Subgroup of A or B

                    Weak antigen during leukaemia

                    Acquired B phenomenon (in group A people)


           3.     Group III Discrepancies:

-  This occurs when extra proteins in plasma cause rouleaux formation or pseudoagglutination.

- Causes:

                     Elevated globulins (e.g. Multiple myeloma)

                     Increased fibrinogen

                     Plasma expanders

                           Wharton’s jelly          


           4.     Group IV Discrepancies:

- This occurs due to miscellaneous causes.

              - Causes:

                       Alloantibody

                       Autoantibody

                       ABO Isoagglutinins

                       Antibodies other than ABO system

                       Polyagglutination

 

  Cases to solve:


 Patient

Anti-A

Anti-B

Anti-A,B

A1 cells

B cells

O cells

Autocontrol

1

4+

-

4+

1+

4+

-

-

2

3+

4+

4+

1+

-

-

-

3

-

-

-

4+

4+

4+

-

4

4+

2+

4+

-

4+

-

-

5

-

4+

4+

4+

1+

1+

1+

6

-

-

-

-

-

-

-

7

4+

4+

4+

2+

2+

2+

2+

8

4+

-

4+

-

4+

3+

-

9

-

-

2+

2+

4+

-

-

10

4+

4+

4+

2+

-

2+

-

 

 




    After identification of a discrepancy, next step is to resolve them to find out definitely the true blood group. That will be     discussed later.