Practical 7: Crossmatch Flashcards

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1
Q

What is the principle behind the antiglobulin test?

A

Commercial antibody with a specificity toward human
globulins is used to agglutinate antibody-coated (or complement) RBCs

Reagent contains antibodies toward:
* IgG (anti-IgG) and/or
* Complement (anti-C3d, anti-C3b)

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2
Q

What’s the principle and procedure behind the indirect AHG
(3)

A

Detects IgG or complement bound to RBCs

Two-step procedure:
* Antibodies (in serum) are incubated at 37° C with RBC
antigens in vitro

  • RBC suspension is washed and then combined with AHG reagent to detect agglutination
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3
Q

What are the uses for IAT
(4)

A

Antibody screening
Antibody identification
Crossmatching
Antigen typing

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4
Q

What is the purpose for crossmatching?

A

Determines serologic compatibility between donor and patient before transfusion

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5
Q

What happens if washing goes wrong in IAT?

A

Free IgG remains and interferes with AHG binding to Red Cell bound IgG causing a
False Negative as all AHG bound to free IgG and no excess to crosslink coated cells

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6
Q

What should you do if you have negative crossmatches with the indirect IAT?

A

Add 2 drops IgG Sensitised (a.k.a. Coombs Control Cells) and Centrifuge P5 Read Macro

Should be positive

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7
Q

What is your positive control for IAT in gels

A

Weak Anti-D (25ul) + an (50ul) ORhD Pos Cel

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8
Q

What is your negative control for IAT in gels

A

AB Serum (25ul) + an (50ul) ORhD Pos Cell

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9
Q

What does the DAT do?

A

Detects IgG or complement bound to RBCs
● In the procedure, AHG reagent is added after the RBCs
have been washed
●Agglutination demonstrates whether IgG or
complement was attached to the RBCs

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10
Q

What might cause positive DAT

A

Transfusion reaction
Haemolytic disease of the newborn
Autoimmune haemolytic anaemia
Drug-related mechanism

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11
Q

What factors affect the IAT

A

Ratio of serum to cells
Temperature
Reaction medium: LISS
Incubation time

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12
Q

What are the most common sources of error for the IAT

A

Inadequate washing

Nonreactive AHG reagent

Failure to add AHG reagent
(Green Colour helps)

All negative antiglobulin test
reactions must be checked by
the addition of IgG-sensitized
cells

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