The DAT & pos Auto-controls Flashcards
What’s the purpose of doing an auto control in an Aby ID?
Check for auto-Aby (against self Ag) & allo-Aby (against foreign Ag)
- Allo: Agg. all panel cells & Neg Auto control
- Auto: Agg. all panel cells & Pos Auto control
What reasonbs may an auto control be pos(3)
- HTR from a recent transfusion (e.g. Aby in plasma containing product or less freq Ag on donor RBC)
- Autoimmune haemolytic anaemia (AIHA)
- Aby against testing medium e.g. buffer, gel
When do you need to Ix a pos DAT
Pos DAT WITH signs of haemolysis
Procedure of performing an elution (7)
- Centrifuge & remove as much plasma as possible
- Wash RBC 4-5x & collect last wash
- Add acid/EDTA & incubate 1-2 mins
- Centrifuge cells
- Collect supernatant (acidic) & Adjust pH until neutral
- centrifuge to remove supernatant & transfer eluate to new tube
- Perform Aby ID on eluate and last wash
Why do you need to collect the last wash in an elution
To check the validity of the elution results
- if Neg: Aby rxn in eluate comes from the Aby on the cell
- if Pos: Aby rxn came from the Aby in the plasma
a) Why might you get a pos DAT (mixe field) but a neg Aby screen (from a HTR due to recent transfusion)?
b) what do you do next
a) bc no excess Aby in plasma since bind to donor RBC first
b) Perform elution & Aby ID the eluate
How much should a pt’s RBC inc by in 1 unit of RBC?
inc by 10g/L
a) Why can autoAby of warm AIHA be a problem in phenotyping (AbyID)?
b) whats the solution
a) autoAby can mask alloAby - cause a false pos result for the known Aby being tested (e.g. Jka-Aby), since auto-Aby are IgG, when an anti-IgG is put = cause the cells to agglutinate
b) use IgM typing sera (similar to rvs grouping steps). Avoid using anti-IgG in IAT. Use Saline tube method bc low Sn
WARM &/ COLD AIHA: When is it appropriate to do an autoadsorption (& not)
Do: Pt NOT transfused in past 3 mths bc only there cells in circ
Don’t: pt transfused in past 3 mths bc donor aby might adsorb alloAby bc donor RBC adsorb alloAby * pt’s RBC can’t be used -> alloadsorption
WARM &/ COLD AIHA: what do you do if pt has been trandfused in the last 3 months and you want to remove pts autoAby
perform alloadsorption (donor RBC adsorb alloAby * pt’s RBC can’t be used)
- by using other cells to adsorb the autoAby from plasma
- selected cells should not adsorb cliniclly sig Aby
- consider the phenotype of pt’s RBC = use cells match pt’s
- if pt’s phenotype is not known, use cells thats Ag neg for clin. sig. Aby (Rh, Kell, Duffy, Kidd & MNS Ag)= Allo Aby should remain in at least one tube => elution & ID adsorbed alloAby
WARM AIHA: selecting blood for X-M & transfusion
Select:
- phenotype-matched blood if available
- if alloAby present, select Ag neg blood
X-M:
- using adsorbed plasma (avoid interferance w/ AutoAby)
How are ABO discrepancies resolved in cold agglutinant disease
- FWD rxn: wash cells w/ warm saline
- RVS rxn: prewarmed rxn cells & pt’s plasma. OR use autoadsorbed plasma in indiv. w/ hi titre Aby
How can you differentiate b/w benign & pathological cold AIHA (CAD) in the TM lab (*to expand on methods later)
- Aby titration studies
- THermal amplitude studies
- Transfuse blood warmer
What’s the difference b/w warm & cold AIHA & mixed type AIHA
Warm: IgG
Cold: IgM, C3d
Mixed: IgG + IgM (lower titre), C3d
Difference b/w Benign & pathological cold AIHA
Benign: low titre, bind @ 4C or RT (weak RVS rxn)
Pathological: high titre (>1000), REACT up to 32C,
* both IgM & usually autoanti-I
