Intro to blood group serology

Question 1

Genetic control of blood groups - the two types of determinants

Answer 1

Protein - gene codes for the antigenic determinant itself - Rh, Kell, Duffy, Kidd systems
Glycolipid - gene codes for production of enzymes that add or remove carbohydrates or lipids - ABO, lewis group systems

Question 2

Functional aspects of blood group antigens

Answer 2

• Duffy blood group system and malaria - duffy antigen acts as entry point for malaria into RBC’s, in caucasians null phenotype rare, black african ethnics up to 40% have null phenotype (natural selection for resistance)
• The McLeod phenotype, Kx null phenotype associated with chronic granulomatous disease and acanthocytosis

Question 3

what is the most likely reason for having different blood groups

Answer 3

genetic drift, can monitor patterns of migration, need migrants to donate blood so rare types in their population can be supported

Question 4

Rh(D) types - ethnic differences

Answer 4

17% caucasians -ve

<1% Polynesians -ve

Question 5

Kidd types - ethnic differences

Answer 5

<0.01% in caucasians

1% in Polynesians

Question 6

MNS system - the U phenotype

Answer 6

only in black african ethnic background

Question 7

The 3 types of antibodies

Answer 7

IgM IgG IgA

Question 8

Naturally occurring antibodies

Answer 8

No exposure to foreign red cells but exposure to red cells containing A and B like antigens

Question 9

Immune occurring antibodies

Answer 9

Exposure to foreign red cells e.g. Rh+, by transfusion or pregnancy

Question 10

Naturally occurring red cell antibodies

Answer 10

Develop in the absence of exposure to the red cell antigen
Stimulated by cross reacting antigens derived from bacteria
Not present at birth but develop during the first year of life
Usually glycolipid
Significant IgM component to antibody but IgG may also be present
ABO and lewis antigens
Ability to activate compliment
Intravascular site of red cell destruction

Question 11

Immune stimulated red cell antibodies

Answer 11

Usually glycoprotein
develop only following expose to specific antigen
produced following - transfusion, pregnancy, injection
normally IgG in nature
Extravascular sie of red cell destruction

Question 12

ABO antigens distribution

Answer 12

widely distributed: blood cells, epic cells, body fluids

Question 13

ABO phenotype determined by

Answer 13

glycosyltransferase enzymes, responsible for addition of CHO molecules to basic membrane structure
H antigen nessecary for ABO phenotype to be expressed

Question 14

What is the terminal sugar for each ABO antigen?

Answer 14

A = N acetyl galactosamine 
B = D galactose 
O = Nil

Question 15

ABO incompatible transfusion leads to?

Answer 15

Intravascular haemolysis, renal failure, DIC = disseminated intravascular coagulation

Question 16

Universal recipient, donor and whether their rare or common?

Answer 16

Donor = O common
Recipient = AB rare

Question 17

Rh blood group system, summary

Answer 17

discovered in 1939, protein dominant, expression only on red blood cells, antibodies produced following immune stimulation, highly immunogenic particularly Rh(D) –> if you transfuse a D- individual with D+ red cells 80-90% will form anti D

Question 18

What is anti D

Answer 18

an IgG antibody that is unable to bind complement, red cell destruction is extravascular
most common cause of haemolytic disease of new born

Question 19

protocol for transfusion of Rh(D) cells

Answer 19

normally transfuse cells of same type as recipient

Never transfuse positive cells to negative woman of childbearing age

Question 20

alleles producing the Rh antigen

Answer 20

3 genetically closely linked alleles 
C and c
D and d
E and e 
the 3 allelic agents usually behave as a single entity, a number of common alleles can thus be defined

Question 21

Minor blood group systems

Answer 21

over 400 blood group systems have been defined

majority only of theoretical interest

Question 22

Factors involved in the clinical importance of blood group systems

Answer 22

frequency of antigen in population
frequency of antibody production following transfusion of red cells containing antigen (immunogenicity)
Ability of antibody to destroy transfused red cells

Question 23

Commercially sourced monoclonal antibodies

Answer 23

for antigen testing
high sensitivity and specificity
are IgM in nature
produce direct agglutination

Question 24

Zeta potential

Answer 24

distance between red cells as they are negatively charged and so repel each other
IgG molecule too small to produce cross linking and hence a potentiator needed to produce agglutination e.g. antihuman globulin or enzymes such as albumin

Question 25

Haemolytic disease of newborn

Answer 25

when material antibody crosses placenta, destruction of fatal red cells
Always involves an IgG antibody
most commonly caused by anti D, then Anti c then anti kill
Frequencies greatly reduced by introduction of immunoprophylaxis

Question 26

antenatal prophylaxis

Answer 26

still birth with hyropsfetalis caused by Rh antibodies

Question 27

Infant with kernicterus - mechanism

Answer 27

brain damage caused by jaundice
- born alive with maternal antibodies in babes plasma for several weeks, infant continues to produce D positive red cells which are destroyed by anti D, babe becomes jaundiced after birth, doesn’t happen in utero because bilirubin sucked out into maternal circulation, infant BBB not well developed, bilirubin cross into CNS neurological irritant and abnormalities e.g. cerebral palsy

Question 28

Prevention of Rh(D) HDN

Answer 28

RhD Ig immunoglobulin given routinely after birth of an Rh(D)pos baby to an RhD neg mum
Kleehauer test used to detect women with larger fetomaternal bleeds
Anti D Ig given during pregnancy following potentially sensitising event
- Abortion
- termination
- Amniocentesis
Routine antenatal prophylaxis

Question 29

Why is ABO haemolytic disease of newborn rare?

Answer 29

AB antigens weakly expressed in the foetus and newborn

Ab antigens widely distributed in placental tissue and absorb antibody before it reaches fetus