Practical 5: Unexpected blood group antibodies Flashcards
What is an antibody screen
A test used to detect antibodies
What are antibody screens used on?
(4)
Patients needing a transfusion
Pregnant women
Patients who have had transfusion reactions
Blood and plasma donors
Why do we have to detect antibodies to blood group antigens other than ABO antibodies
We need to detect antibodies of clinical significant i.e. those active at 37 degrees
How do we carry out an antibody screen?
Test the patients plasma/serum against a panel of (3) cell of regent red cells with a known antigen profile
These antigens are listed in the antigen profile sheet
What does a green tinge to gel wells mean?
There is anti-human globulin present
Why do plasma -> antigen tests vary in strength?
A homozygous reaction is stronger than a heterozygous antigen reaction
What are the two classifications of unexpected antibodies?
Clinically significant (igG)
Not clinically significant (IgM)
What are clinically significant unexpected antibodies associated with?
Haemolytic transfusion reactions
Haemolytic disease of neonate
Explain how an antibody screen is carried out
Patients plasma/serum is incubated with screening cells
An indirect antiglobulin test is performed using anti-human globulin reagent
This allows us to detect any igG to the antigens on the commercial reagent cells
What are our screening cells?
(5)
Cells from single donor group O cells
They are not pooled
Group O cells are used so that anti-A and anti-B antibodies will not react
They come in sets of 2 or 3 vials each
Each vial has been phenotyped for each antigen
What do the screening cells come with?
An antigram
What is an antigram
This is a sheet of paper that will list the antigens present in each reagent donor vial
What do potentiators do?
They enhance an antigen-antibody reaction
Give five examples of potentiators
Saline
Low-ionic-strength solution (LISS)
Bovine serum albumin (BSA)
Polyethylene glycol (PEG)
Proteolytic enzymes
What is the downfall of using saline as a potentiator?
May only enhance the reaction if incubated for a long time
What is the preferred potentiator
Low-ionic-strength-saline
What is the main benefit of LISS
Increases Ab-Ag binding rate and decreases incubation time from 1 hr to 15 mins
Why might proteolytic enzymes not be considered the best potentiator
They can destroy some antigens
Why is it important to know the patient history before carrying out a transfusion
Some diseases are associated with antibodies
Patient may have come from another hospital where they were previously transfused
Some antibodies occur at a higher frequency in some races
Mixed RBC populations from a previous transfusion can remain for up to 3 months
In your own words how would you carry out an antibody screen?
(6)
Get your green tinged gel, sample and pipette
Pipette 50ul of the 0.8% red cell suspension of screening cells into each well of the gel
Add 35ul of the test serum or plasma to each microtube
Incubate at 37 degrees for 15 minutes
Centrifuge for 10 minutes
Record results
