DAT Flashcards
Distinguish between IAT and DAT
IAT: in vitro, test what has attached to cell in test system
DAT: in vivo, test what has attached to the cell in the body
When is DAT ordered?
- Hemolysis present
- Positive auto-control
- Transfusion reaction workup
- Cordblood eval
DAT is predictive of ____ by immune process in 83% of the population exhibiting symptoms
Hemolytic anemia
Interpretations of positive auto-control
- DAT could be positive for IgG
- Transfused cells are in pt sample
- Autoimmune process
- Contamination of AHG procedure
- HDN/HTR
- Drug-induced Ab
Interpretation of negative auto-control
- DAT likely negative for IgG
- Ab not reactive with pt’s own cells
- Could be IgA or IgM or undetectable proteins
- Weak reaction, Ab dissociated from cell
- Complement could have destroyed cells before reaction
Principle of DAT
- Uses anti-human globulin (against Fc portion of antibody) to detect presence of Ab on the RBCs themselves
- No incubation step (no LISS inc)
Implications if check cells don’t work
Not enough washes
Inert control
Pt RBCs that you didn’t add AHG reagent to -> expect no agglutination bc cells shouldn’t be spontaneously clumping
AHG reagent
- polyspecific anti-human-globulin
- human/rabbit IgG + murine monoclonal anti-C3b, C3d (anti-complement)
Check cells in DAT
- Coomb’s control cells with anti-IgG
- Complement control with C3 attached
Why can failure to add AHG reagent quickly cause false negative?
Because complement/IgG can start to fall off the cell and dissolve in the plasma
In order to be a DAT, it must detect what?
Both complement and IgG on cell
Possible reasons for positive anti-C3b, C3d reaction
- HTR
- Drug-induced Ab
- Cold autoimmune anemia
- Complement activation due to bacterial infection or auto-Ab
Possible reasons for positive anti-IgG reaction
- HTR from allo-Ab
- HDN
- Drug-induced Ab
- Warm autoimmune anemia
PCH
Donath-Landsteiner IgG auto-Ab reacts with RBCs in the coldest parts of the body, which causes irreversible complement binding
Cold Agglutinin Syndrome (CAS)
Cold-reactive IgM auto-Ab binds complement as RBCs return to warmer part of the body, when IgM dissociates and leaves RBCs coated with complement
Warm Autoimmune Hemolytic Anemia (WAIH)
Auto-Ab reacts with patient’s RBCs in vivo, may or may not activate complement
Biggest reason to perform elution?
ONLY when positive DAT with anti-IgG!
Not positive DAT and anti-C3d! Need the anti-IgG!
Reasons to do elution
- Positive DAT and anti-IgG
- HTR workup
- HDN
- Confirm presence of specific Ag on RBCS, use in conj. with adsorption
- Confirm Ab specficity by showing it can be adsorbed onto RBC of only a particular blood group phenotype
Elution principle
Remove and ID Ab coating red cells
Elution steps
- Wash 20 drops of whole blood cells 4x
- Remove IgG from cell
- Make solution containing antibody testable for cells
- Perform Ab ID
In elution, what do you destroy and preserve?
Destroy cells, preserve Ab
Why do you save the supernatant from the last elution wash?
- To test it against screen or panel cells in the same method as eluate -> expect negative result
- Positive result = invalid
Interpretation of negative elution results
- Non-RBC Ab
- Low incidence IgG
- Weak IgG
