AHG Flashcards
Exam 1
What is the main difference between the IAT and the DAT test?
The IAT test detect in-vitro sensitization and the DAT test detects in-vivo sensitization
What is the difference between polyspecific AHG and monospecific AHG?
Polyspecific: includes antibodies to IgG and C3d, Monospecific: only includes antibodies to either IgG or C3d
What is the difference between polyclonal and monoclonal antibodies?
Polyclonal: is a mixture of antibodies from different plasma cell clones that recognize multiple epitopes, Monoclonal: antibodies that are from one clone of plasma cells that recognize a single epitope
Describe the basic steps of the DAT test.
The patient’s RBCs (which are already coated with antibody in-vivo) are washed and incubated with antihuman antibodies (anti-IgG, anti-C3d). If agglutination occurs, then the patient’s red cells are coated with either antibodies or complement depending on which reagent gives a positive reaction.
What conditions have a positive DAT that this test could help diagnose?
Hemolytic Disease of the Fetus and Newborn, Hemolytic Transfusion Reaction, Autoimmune Hemolytic Anemia
Cold autoimmune hemolytic anemias usually only react when tested with _______. (anti-IgG or anti-C3d). Why?
Anti-C3d. This is an indirect way of detecting IgM antibody that is bound to the red cell that has also bound complement.
Describe the basic steps of the IAT test.
Antibodies (patient plasma or antisera) is mixed with red cells (reagent/donor/patient). During incubation, the antibody forms antigen-antibody complexes if the antigen/antibodies are both present. The cells are washed and anti-IgG is added to enhance the reaction. The tube is then read for agglutination.
What is the purpose of washing the red cells before adding the anti-IgG?
Removes any free globulins to which the anti-IgG could attach.
What is the purpose of adding check cells to all negative reactions?
The check cells should agglutinate when they react with the unbound anti-IgG. If they do not agglutinate, we know that the unbound anti-IgG bound with free globulins that were not adequately washed away. Therefore, the negative reaction may have been a false negative.
What is the purpose of compatibility testing and which test (DAT or IAT) is performed during compatibility testing?
IAT, it tests patient plasma (antibodies) against the donor red cells (antigens) they are to be transfused. If agglutination occurs, then the patient has an antibody to one of the donor’s antigens and the unit is incompatible with the patient.
What is the purpose of the antibody screen?
The antibody screen is used to detect if the patient has any antibodies in their plasma. By testing against 2-3 known reagent cells, it can be determined if the patient has an additional antibody. If agglutination occurs with one of the cells, additional testing will need to be performed to identify the antibody.
What concentration of red cells should be used when performing the IAT or DAT test?
3-5%
Describe the postzone and prozone effects.
Postzone: excess antigen preventing agglutination, Prozone: excess antibody preventing agglutination
What is the zeta potential and how is it created?
Zeta potential is the difference in charge density between the inner and outer layers of the ionic cloud, it is created because red cells have a net negative charge from the sialic acid which attracts the positively charged cations to form a layer around the red cells
What issue does the zeta potential cause in testing?
Antibodies are positively charged and are repelled by the positive layer of cations around the red cell, this makes agglutination more difficult to achieve
