Goals of transfusion science
- Avoid HTR
- Replace lost blood
- Test for compatibility
- replace lost blood
- prevent sensitisation of RBC
allo-Ab vs auto-Ab
- Allo- : non-self Ag
* Auto- :self- Ag
Ab made @ 1º or 2º response
1º: Igm
2º: IgG = Anamnestic response
characteristic of IgM Ab
- Naturally occurring* or immune
- react optimally @ RT
- activate complement
characteristic of IgG Ab
- Immune
- React optimally @ 37ºC
- some can activate complement
Describe the haemagglutination of IgM & IgG Ab
- RBC are separated 20nm from each other due to zeta potential
- IgM: direct agglut. bc big enough (30nm) - can crosslink w/ adjacent RBC w/out being affected by the repulsion forces of ZETA
- IgG: indirect bc can’t be used for agglutination alone (12nm)
Compare and contrast the IAT and the DAT (coombe’s test)
- IAT: detects if Ab in plasma binds to RBC in vitro
- DAT: detects Ab &/or C3d bound to patient RBC in vivo
- DAT don’t need to be incubated
When are DAT & IAT used?
- IAT: Ab screening & identification, cross-matching, phenotyping
- DAT: Haemolytic transfusion reactions (HTR), Haemolytic disease of new born (HDNB)
Describe the principles of CAT (column agglu. tech.) / card assay
- CAT: column agglutination tech.
- High density solution over sephadex beads/matrix
- reagent Ab can be incorporated in the beads
explain the steps & the principles of SPRCA assay
- RBC added & lysed - sticking on walls of well
- LISS & plasma added
- Ab bind to Ag on lysed RBC
- Indicator cells (cells w/ a-IgG Ab) bind to Ab
- centrifuge
Advantages & disadvantages of CAT /card method
Adv:
- Inc sensitivity
- stable for 24hrs
- washing not required
- can be automated
- AHG control cells not required
Dis:
- $$$ w each card & equipment
Advantages & disadvantages of CAT vs SPRCA method
Adv:
- only detect IgG
- Inc sensitivity
Dis: detects non-specific RBC Ab
Causes of false pos in control tube of CAT assay- supposed to be negative
- very Hi [RBC] - must be 1% cell suspension
- expired card
- Fibrin in sample
- not centrifuged long enough
- Wharton’s jelly
explain the steps CAT /card method
- 0.8-1% cell suspension
1. 50uL cells (+ 50uL plasma) added to column
2. centrifuged
3. Agglutinated cells trapped @ top of gel matrix
4. if not agglutinate cells move through gel to the bottom
Difference b/w/ grading & scoring rxns
G = Sc 4+ = 12 3+ = 10 2+ = 8 1+ = 5 w = 3 0 = 0
Why are AHG control cells added to the AHG test
- checks that AHG is working (see agglutination) = valid ie. no agglutination means that IgG is not bound to RBC & not due to dysfunctional AHG reagent
- ensure AHG not binding to free Ab (when not washed properly)
- AHG reagent addded
allelic gene
gene that varies @ specific locus
consequence of Ag/Ab binding (IgM vs IgG)
- Complement activation: IgM, intravascular heamolysis
- Ab-dependent cell-mediated cytotoxicity (ADCC): IgG, extravascular haemolysis (spleen)
=> haemolytic transfusion reaction (HTR)
=> haemolytic disease of newborn (HDNB)
Understand what haemagglutination is and how it is used in the transfusion
laboratory*
- clinically sig Ab detect
