W11TL7 - Antibody Identification

Question 1

Why do people have antibodies?

Answer 1

Naturally occurring antibodies
- i.e. ABO antibodies
Immune antibodies - produced after exposure to the corresponding antigen
Passively acquired antibodies
- administered i.e. prophylactic anti-D, IVIg, donor plasma/platelet
Pregnancy
- foetal RBCs are exposed to the maternal circulation during childbirth
- higher incidence of alloantibody production in females
Transfusion
- < 1% - 8% of individuals who are “incidentally” transfused produce an alloantibody
- up to 40% of individuals who are chronically transfused produce an alloantibody
Exposure to foreign blood via other sources
- i.e. sharing of needles by IV drug users, etc

Question 2

Most Common Antibodies

Answer 2

85% single aby, 15% multiple antibodies
Ant-D (13.6%), -E (16.8%), -C (8.4%), -c (3.7%)
Anti-K (10.3%)
Anti-Fya (4.2%)
Anti-S (1.9%)
Anti-Jka (1.4%)
Anti-M (15.0%)

Question 3

When to Expect an Antibody is Present

Answer 3

Positive antibody screen
ABO grouping discrepancy
- “cold” antibody (IgM), such as anti -M, -N, -P, agglutinating A / B cells used in the reverse group
Incompatible cross-match after negative antibody screen
- anti-ABO antibody
- antibody against a low-incidence antigen

Question 4

Auto Control

Answer 4

React patient cells against patient plasma
If negative, patient has an alloantibody
If positive, patient has an autoantibody (+/- alloantibody)

Question 5

Phenotyping

Answer 5

React patient RBCs with known antibody
- the known antibody is IgG or IgM
- i.e. react patient A’s RBCs with anti-M antibody
For controls, need to ensure that the system can detect the weakest examples of antigen expression
Positive control
- RBCs which have heterozygous expression of the target antigen
i.e. M+N+
Negative control
- RBCs which do not express the target antigen
- i.e. M-N+

Question 6

Reaction Grades

Answer 6

A single antibody will give the same reaction grade against multiple cells
Exceptions:
- antibody demonstrating dosage (i.e. anti-Jka)
- antibody reacting against an antigen that has variable expression (i.e anti-P1)
Multiple grades in a cell panel indicates:
- a single antibody demonstrating dosage
- multiple antibodies present in the sample

Question 7

High Incidence Antigens

Answer 7

Present in > 98% of the population (e.g. k, U, Kpb, Jsb, Lub, Coa)
Antibodies against these are rare
Reacts against most / all cells in the panel, w / negative autocontrol
Autoantibody presents similarly, but auto is +ve
Test cells neg for high incidence antigen:
- enzyme-treated/chemically modified cells
- e.g. DTT destroys Kell and Lutheran ag’s
- rare Rhnull and K0 cells
Phenotype patient cells for presence of high-incidence Ag

Question 8

Antibodies to Low Incidence Antigens

Answer 8

Low incidence antigens - in < 10% of the population (e.g. Kpa, Cw, Lua, Jsa, Dia)
Antibodies are uncommon
Not identified on screen (and therefore not routinely ID’d)
Found in combination w/ other aby, or after an incompatible XM w/ a neg screen
Send to Red Cross for ID
Easy to find blood for transfusion