Transfusion techniques

Question 1

Goals of transfusion science

Answer 1

• Avoid HTR
• Replace lost blood
• Test for compatibility
• replace lost blood
• prevent sensitisation of RBC

Question 2

allo-Ab vs auto-Ab

Answer 2

• Allo- : non-self Ag

* Auto- :self- Ag

Question 3

Ab made @ 1º or 2º response

Answer 3

1º: Igm

2º: IgG = Anamnestic response

Question 4

characteristic of IgM Ab

Answer 4

• Naturally occurring* or immune
• react optimally @ RT
• activate complement

Question 5

characteristic of IgG Ab

Answer 5

• Immune
• React optimally @ 37ºC
• some can activate complement

Question 6

Describe the haemagglutination of IgM & IgG Ab

Answer 6

• 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)

Question 7

Compare and contrast the IAT and the DAT (coombe’s test)

Answer 7

• 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

Question 8

When are DAT & IAT used?

Answer 8

• IAT: Ab screening & identification, cross-matching, phenotyping
• DAT: Haemolytic transfusion reactions (HTR), Haemolytic disease of new born (HDNB)

Question 9

Describe the principles of CAT (column agglu. tech.) / card assay

Answer 9

• CAT: column agglutination tech.
• High density solution over sephadex beads/matrix
• reagent Ab can be incorporated in the beads

Question 10

explain the steps & the principles of SPRCA assay

Answer 10

1. RBC added & lysed - sticking on walls of well
2. LISS & plasma added
3. Ab bind to Ag on lysed RBC
4. Indicator cells (cells w/ a-IgG Ab) bind to Ab
5. centrifuge

Question 11

Advantages & disadvantages of CAT /card method

Answer 11

Adv:

• Inc sensitivity
• stable for 24hrs
• washing not required
• can be automated
• AHG control cells not required

Dis:
- $$$ w each card & equipment

Question 12

Advantages & disadvantages of CAT vs SPRCA method

Answer 12

Adv:

• only detect IgG
• Inc sensitivity

Dis: detects non-specific RBC Ab

Question 13

Causes of false pos in control tube of CAT assay- supposed to be negative

Answer 13

• very Hi [RBC] - must be 1% cell suspension
• expired card
• Fibrin in sample
• not centrifuged long enough
• Wharton’s jelly

Question 14

explain the steps CAT /card method

Answer 14

• 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

Question 15

Difference b/w/ grading & scoring rxns

Answer 15

G = Sc
4+ = 12
3+ = 10
2+ = 8
1+ = 5
w = 3
0 = 0

Question 16

Why are AHG control cells added to the AHG test

Answer 16

• 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

Question 17

allelic gene

Answer 17

gene that varies @ specific locus

Question 18

consequence of Ag/Ab binding (IgM vs IgG)

Answer 18

• Complement activation: IgM, intravascular heamolysis
• Ab-dependent cell-mediated cytotoxicity (ADCC): IgG, extravascular haemolysis (spleen)

=> haemolytic transfusion reaction (HTR)
=> haemolytic disease of newborn (HDNB)

Question 19

Understand what haemagglutination is and how it is used in the transfusion
laboratory*

Answer 19

• clinically sig Ab detect