Antibody screening identifies the specificities of antibodies causing positive serological crossmatch
SPECIMEN: Serum + screening cells
Antibody screening is a key process in pre-transfusion compatibility testing.
It is one of the principal tools for investigating potential hemolytic transfusion reactions, HDN, and immune hemolytic anemia
Detects alloantibodies, which are antibodies against someone else’s red blood cells.
Autoantibodies may complicate detection. If there is presence in their plasma or serum, it complicates detection because it does not mean that it will cause hemolytic reaction.
Cause of Hemolytic reaction are antibodies of patient that targets the donor or someone else's red blood cells.
Autoantibodies can cause positive screening
Tube technique is routinely performed.
Recipient serum + known RBCs (screening cells)
IS+37°C+AHG
Enhancement media may be used
Enhancement media may be used in tube technique such as LISS, BSA, PEG, in order to facilitate antigen-antibody binding
In tube technique, there is hemolysis or agglutination in any phase.
In order to observe hemolysis or agglutination, we have to use serum as a plasma
RBC reagents
2-5% in preservative diluent
Packaged in sets of 2-3 cells with varied antigen expression.
Accompanied by antigen profile sheet
Antigen profile sheet is used for basis or guide in antigens present in screening cells
22% Albumin is an enhancement media that reduces zeta potential
Zeta potential is the net negative charge present in red blood cells membrane.
Works to repel other red blood cells from one another to avoid clumping during circulation
Makes your red blood cells comes together so that they will be agglutinated by your antibodies
Low ionic strength solution is an enhancement media which is a glycine in an albumin solution.
It increases uptake of antibodies onto RBC surface
Polyethylene Glycol is an enhancement media that removes water in test system thereby concentrating any antibodies present
Makes the RBC surrounding hydrophobic so that they can easily take up the antibodies
Not appropriate for recipients with increased plasma proteins
Generally more sensitive than LISS and albumin
Be very careful in using PEG enhancement media because it can cause non-specific aggregation of cells (centrifugation after 37°C is omitted) and has a high chance of producing a false agglutination
AHG reagents brings the non-agglutinating antibodies together.
In order to visualize antigen-antibody binding, we add AHG reagents for us to see the presence of non-agglutinating antibodies in reaction vessel
Polyspecific AHG
Polyvalent or broad-spectrum Coombs serum
Components:
Anti-IgG
Anti-C3/C4 or Anti- C3d/C3b or Anti-IgM
Monospecific AHG
Components
Anti-IgG or Anti-C
Coombs control cells are basically red blood cells with attached anti-D antibodies in their D antigen
D(+) RBCs coated with anti-D
Used to verify if the negative AHG is valid
Agglutination or hemolysis in any of the phase
NEGATIVE (0) = the patient has no antibodies against the antigens present in the screening cells
POSITIVE (+1 to +4) = complete hemolysis (+4)
IgM antibody allows reaction of cold reacting antibodies, which is detected in IS phase
Polyspecific AHG detects IgM antibody if the AHG contains anti-complement activator