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Blood Grouping and Compatibility Testing (Indirect antiglobulin test…
Blood Grouping and Compatibility Testing
ABO grouping
Dependent upon antibody-antigen interactions
Test: patient red cells with monoclonal antisera
Done in precipitin tubes, microtitre plates or gel column
Monoclonal antisera
Monoclonal antibodies exhibit high degrees of potency and specificity
Anti-A reagent dyed blue
Anti-B dyed yellow
Reverse typing
If only plasma or serum sample:
Mix with known red cell type
Group A plasma has Anti-B that will agglutinate group B cells
Gel column
agglutinate can't pass through column so sits at top if recognition of Ab
if they don't bind then they pass through column
Conditions
3% suspension of washed red cells
room temp incubation
control cells and anti-sera
need to grade agglutination
Problems
Clots can be misread
Rouleaux- red cells stacked on top of each other, associated with old samples
Plasma/serum has opposite antigens to that on the red cells so group a will agglutinate B cells in plasma
Compatibility testing
Need to test potential interactions between donor red cells and patient serum
if patient had pervious transfusion may have raised IgG antibodies against certain Rh antigens
may undergo hameolytic reaction
Indirect antiglobulin test
Set up reaction between patient serum and red cells
Step 3 wash cells so complex still there then add anti human Ig Coating of red cells by compliment or antibody before wash
Anti human Ig will cross link with complex and cause agglutination of red cells
Cells washed after step 3
all incubations at 37
Low ionic strength saline (LISS) reduced incubation time
Procedure
Donor cells suspended in LISS, incubated at 37 for 10-30mins
washing necessary if column agglutination not used
Add anti human globulin causes bridge between sensitised red cells, allowing agglutination
AHG (anti human globulin)
polyspecific reagent containing anti-human polyclonal IgG raised in animals
contains monoclonal anti-c3D
polyclonal IgG will recognise any antibody in plasma
If positive
Ab Screen
helpful to include techniques such as
enzyme treated cells
saline room temp techniques
+ve obtained specificity determined by reacting serum against panel of red cells of known phenotypes
Direct Coombs Test
A test to see if your red cells are already coated in Ab
Done after transfusion
Investigating blood transfusion reactions
Immediate spin crossmatch
Donor Red cells suspended in saline
incubated with patient plasma for 2-5mins
centrifuged
examined for agglutination
designed to detect only ABO incompatibility
false -ve's if Ab titres low
false +ve's if rouleaux or cold reacting Ab's