Practical 5: Unexpected blood group antibodies

Question 1

What is an antibody screen

Answer 1

A test used to detect antibodies

Question 2

What are antibody screens used on?
(4)

Answer 2

Patients needing a transfusion

Pregnant women

Patients who have had transfusion reactions

Blood and plasma donors

Question 3

Why do we have to detect antibodies to blood group antigens other than ABO antibodies

Answer 3

We need to detect antibodies of clinical significant i.e. those active at 37 degrees

Question 4

How do we carry out an antibody screen?

Answer 4

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

Question 5

What does a green tinge to gel wells mean?

Answer 5

There is anti-human globulin present

Question 6

Why do plasma -> antigen tests vary in strength?

Answer 6

A homozygous reaction is stronger than a heterozygous antigen reaction

Question 7

What are the two classifications of unexpected antibodies?

Answer 7

Clinically significant (igG)

Not clinically significant (IgM)

Question 8

What are clinically significant unexpected antibodies associated with?

Answer 8

Haemolytic transfusion reactions

Haemolytic disease of neonate

Question 9

Explain how an antibody screen is carried out

Answer 9

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

Question 10

What are our screening cells?
(5)

Answer 10

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

Question 11

What do the screening cells come with?

Answer 11

An antigram

Question 12

What is an antigram

Answer 12

This is a sheet of paper that will list the antigens present in each reagent donor vial

Question 13

What do potentiators do?

Answer 13

They enhance an antigen-antibody reaction

Question 14

Give five examples of potentiators

Answer 14

Saline

Low-ionic-strength solution (LISS)

Bovine serum albumin (BSA)

Polyethylene glycol (PEG)

Proteolytic enzymes

Question 15

What is the downfall of using saline as a potentiator?

Answer 15

May only enhance the reaction if incubated for a long time

Question 16

What is the preferred potentiator

Answer 16

Low-ionic-strength-saline

Question 17

What is the main benefit of LISS

Answer 17

Increases Ab-Ag binding rate and decreases incubation time from 1 hr to 15 mins

Question 18

Why might proteolytic enzymes not be considered the best potentiator

Answer 18

They can destroy some antigens

Question 19

Why is it important to know the patient history before carrying out a transfusion

Answer 19

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

Question 20

In your own words how would you carry out an antibody screen?
(6)

Answer 20

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