cls 3311 agh
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CLS 3311 Advanced Clinical ImmunohematologyAntihuman Globulin Testing (AHG)
Antihuman GlobulinDefinition: Antihuman: antibodies against human antigens Globulin: all antibody molecules are globulinsTherefore: Antihuman Globulin is antibody directed against the Fc portion of human antibodies and/or complement components.
Antihuman Globulin In the past AHG was made by injecting rabbits (or sheep, etc.) with human globulin and complement (C). The rabbit would then make antibody to the human globulin and C components.
The antihuman antibody (polyclonal) would then be harvested, fractionated and purified for use in the blood bank as anti-A, anti-B, etc. Each lot # was quite unique. Today we use, almost exclusively, Monoclonal AHG produced using mouse hybridoma cells to make very specific AHG. Figure 4.1, page 75 Harmening
Antihuman Globulin Reagents1. Polyspecific: 1. Contains anti-IgG and anti-C3d (Complement) 2. Contains only one specificity: either antiIgG or anti-C3d. NOT both, only one.
Table 4.1, page73 Harmening
AHG Reagents Include: Anti-IgG (Anti-IgG) Anti-C (Anti-C3/C4) Anti-IgG & C (Polyspecific AHG) These Anti-Human Globulins must be diluted to achieve optimum reactivity. In doing this anti-IgM is diluted BELOW detectable level. The presence of IgM on the RBC is NOT detected using AHG reagents.
Rabbit polyclonal has anti-IgG, -C3d; rabbit/murine monoclonal blend has rabbit Polyspecific (rabbit polyclonal, rabbit/murine monoclonal blend, murine polyclonal anti-IgG and murine monoclonal anti-C3b, -C3d; murine monoclonal) monoclonal has monoclonal anti-IgG, -C3b and -C3d
Monospecific anti-IgG (rabbitpoly- clonal; IgG heavy chains; monoclonal IgG)
Rabbit polyclonal has only anti-IgG; IgG heavy chains only has antibody to gamma chains; monoclonal has murine anti-IgG Contains only antibodies against
Anti-C3d and anti-C3b or Anti- designated Complement components with C4b, -C4d, -C3d (rabbit polyclonal) no anti-immunoglobulin activity Anti-C3d or anti-C3b, -C3d(murine monoclonal) Contains only antibodies against designated Complement components with no anti-immunoglobulin activity
Table 12.1, page 260, AABB Technical Manual, 13th Edition
AHG Techniques: What is the relevance? Some very clinically significant unexpected antibodies (Kidd, Duffy, etc.) attach to red cell antigen or activate complement to do so, but do NOT cause agglutination at immediate spin or 37o phase. Yet, these antibodies are capable of causing severe hemolytic transfusion reactions or hemolytic disease of the newborn.
Relevance of AHG AHG techniques enable the detection of these antibodies or C components that otherwise went undetected. AHG enables detection of both in vitro (Indirect Antiglobulin Test) and in vivo (Direct Antiglobulin Test) antibody attachment.
AHG testing is the primary method of detecting all Antibodies except those of the ABO System.
Expected Vs. Unexpected AntibodiesExpected Antibodies If an ABO antigen is missing from an individuals red blood cell membrane then it is EXPECTED that the individual will produce an antibody to that antigen. These have also been called naturally occurring. Example: Group A individual does NOT have B antigens on their red blood cell membrane. They will normally produce anti-B antibodies.
Unexpected Antibodies In ALL other blood group systems if the antigen is missing from the red cell, the individual is NOT expected to produce an antibody against it, normally. When these antibodies are produced they are termed UNEXPECTED antibodies. EXAMPLE: An individual lacking the D antigen on their RBC membrane is NOT expected to have anti-D antibodies in their plasma, normally. It requires exposure to the D antigen from a foreign RBC either by transfusion or pregnancy.
CONCLUSION: Only ABO antibodies are expected to be produced in the absence of foreign RBC Ag. All other blood group systems require, with a few exceptions, exposure to a foreign red cell antigen (transfusion or pregnancy) to stimulate production of an unexpected antibody.
Indirect Antiglobulin Test (IAT) Another name is Antibody Screen Patient serum or plasma containing unexpected Antibodies is incubated with RBCs possessing the corresponding antigen (Screen Cells). The unexpected IgG class Antibody will bind to the corresponding RBC Antigen during incubation.
OR The Patients unexpected IgM or IgG class antibody will bind C to the RBC membrane with the corresponding antigen during incubation.
The RBCs are then washed with saline to remove all UNBOUND serum proteins including IgG & C. An Anti-Human Globulin reagent is added to the washed, dry RBC button.
If unexpected antibodies (or C) are present on the red cell membrane AHG will bind and cross link the red blood cells causing agglutination.
Set of Problems1. Even 10 mLs of AHG can be neutralized by a tiny amount of free serum protein. 2. A technologist can forget to add AHG to a test tube. 3. A couple of drops of residual saline can dilute the AHG reagent below detectable levels. Normally people do NOT produce unexpected Antibodies. Therefore the test should normally be negative. HOW DO YOU KNOW A NEGATIVE AHG TEST IS A TRUE NEGATIVE?
Coombs Control or Check Cells Addition of IgG coated red cells to all negative AHG tests is required by AABB Standards for Blood Banks and Transfusion Services for antibody screen and crossmatch tests.
Negative AHG test should contain FREE AHG reagent still capable of binding to IgG coated RBCs If IgG coated RBCs are added to negative test and centrifuged, then the free AHG should bind to them and cause agglutination.
If the Check Cells agglutinate, it indicates three (3) things: The test was adequately washed prior to addition of the AHG reagent. AHG reagent was added to the test tube.
The AHG reagent that was added was in an ACTIVE form.
What agglutinated Check Cells DOES NOT mean! That the test was performed correctly!!Why? Because Patient Serum could have been left out of tube The WRONG Patient Serum could have been added The WRONG test cells could be used Incubation time or temperature may be incorrect Enhancement media (LISS) may not have been added The tube could be mis-labeled The results could be mis-read The results could be recorded incorrectly
Purpose of the IAT The purpose of the Indirect Antiglobulin test is to detect unexpected antibodies in patient or donor serum. Screening test only, not for antibody identification. RBCS used are called SCREEN CELLS Reason: theyre used to screen for unexpected antibodies present in the donor or recipient serum. Use a set of cells - Usually 2 or 3 cells, each cell from a different source/donor so each has a unique phenotype
Purpose of the IATWhat type of cells are used as the Screen Cells? Group O cells Why?
The cells MUST have antigens that most commonly stimulate production of unexpected antibodies (Kell, Kidd, Duffy and Rh). SOURCE OF CELLS: Individual donors with specific phenotypes
DIRECT ANTIGLOBULIN TEST (DAT) DAT tests for in vivo sensitized red blood cells Attachment of antibody or complement in vivo
Problem: Clotted samples still contain serum with Ca++ present so that Ccan be activated non-specifically after collection causing false positive results. Solution: Perform test on EDTA sample. EDTA chelates calcium stopping C activation. The blood in the EDTA sample represents in vivo C activity.
DIRECT ANTIGLOBULIN TEST1. Collect sample in EDTA tube Make 3-4% RBC suspension and wash 3-4 times Cord blood needs additional washing. 2. Take 1 drop of 3-4% RBC suspension and centrifuge to get dry button 3. Add AHG to the dry button If IgG or C attached to the RBCs in vivo, the AHG will cause agglutination (Autoimmune process, HDN) NORMAL RESULT: Negative Again, how do we know that the Negative result is a TRUE Negative?
Application of AHG testing include detection of:1. 2. 3. 4. Hemolytic Anemia's Transfusion Reactions Hemolytic Disease of the Newborn Antibody Screening of donors and recipients 5. Final step in Antibody Identification
This represents a general layout for an Antibody Screen report and suggested interpretation of an IAT without reactivity. Can I report it out as negative? Are we able to detect all unexpected antibodies with this system?
I IS 37 LISS AHG CkCells 0 0 0 +
II 0 0 0 +
III 0 0 0 +
Auto 0 0 0 +
No Unexpected Antibodies Detected
Why do we suspect that this unexpected antibody is IgG class? Why not IgM? Is it clinically significant?
I IS 37 LISS 0 1+
II 0 0
III 0 0
Auto 0 0
Unexpected antibody of Class IgG.
IS37 LISS AHG CkCells
00 0 +
00 0 +
00 0 +
Must know what AHG reagent used. If antiIgG, then unexpected IgG class antibody;
If anti-IgG, anti-C3, then coating IgG or Complement Dependent antibody detected.
IIS 37 LISS AHG CkCells 1+ 2+ 4+
II0 0 0 +
III0 0 0 +
Auto0 0 0 +
1. Unexpected antibody detected, IgG class Strong reacting 2. Unexpected antibodies, may be multiple (IgM and/or IgG) detected.
IIS 37 LISS AHG CkCells 1+ 0 0
II0 1+ 2+
III0 0 0
Auto0 0 0
+ + + Unexpected antibodies Interpret detected, one of IgM class and one of IgG class
IIS 37 LISS AHG CkCells 0 2+ 4+
II0 W+ 1+
III0 0 0
Auto0 0 0
+ + May indicate Multiple antibod