L6. ABO and Rh D

Question 1

What are blood group antigens, the two types and give examples.
Compare the genetic determination and inheritance of both

Answer 1

Antigens are glyco proteins/lipids which present on RBC surface + other tissues like vascular surfaces.

1. Protein determinants where gene codes for antigenic determinant itself: eg. Rh, kell, duffy, kidd
2. Glycolipid determinant
   where gene codes for production of an enzyme which add or remove carbohydrates or lipids to cell surface
   eg. ABO, lewis group

Most are autosomal co-dominant inherited (except for Xg which is sex linked)

Question 2

What is one disease associated with duffy antigen (Fya, Fyb) and one with kell antigen (Kk)

Answer 2

1. duffy antigen acts as a binding point for malaria making absence of duffy a and b higher in populations that have endemic malaria
2. kx null phenotype is associated with chronic granulomatous disease and acanthocytosis - all found on same length of chromosome

Question 3

What exposure causes

naturally occurring vs immune stimulated production of antibodies to RBC antigen mean

Answer 3

1. Antibodies develop in first year of life because of absence of exposure to red cell antigen due to blood group and cross reacting antigens derived from bacteria
2. Antibodies only develop after exposure to a specific antigen on foreign RBC
   - eg. in transfusion, pregnancy (Rd), injection.

Question 4

What are the type of antigen, main antibody, complement activation and where RBC damage is caused (haemolysis)

between naturally occuring vs immune stimulated red cell antibodies

Answer 4

1.a) Naturally occurring 
antigen is usually glycolipid.
b) usually use IgM (+/- IgG)
c) activates complement leading to 
d) intravascular RBC destruction 

2. a) Immune stimulated is usually glycoprotein
   b) IgG
   c) No complement activation (or only until early phase (C3))
   d) extravascular RBC destruction - liver, spleen, placenta etc

Question 5

Where are the ABO antigens found and what enzyme does its gene code for and what does it need to be expressed

Answer 5

ABO antigens found in blood, epithelial/endothelial cells and body fluids

Different types of Glycosyltransferase enzymes add Carb to H-antigen expressed on cell surface. Needs this H-antigen

Question 6

What are the consequences of incompatible transfusion

Answer 6

1. Complement activation –> intravascular haemolysis
2. Renal failure
3. Disseminated intravascular coagulopathy: triggering extensive microclotting leading to using up clot factors and then excessive bleeding

Question 7

What alleles are involved in Rh(D) antigen production (found only on RBC)
and which is the most important and why

Answer 7

Rh antigen is product of 3 genetically linked alleles
C and c
D and d
E and e.

Rh(D) is most important as d antigen is an amorph so there is Rh (D) positive and Rh (D) negative (17% caucasian). Immune stim of Rh (D) negative leads to potent IgG antibody production leads to haemolytic disease of newborn.

So plasma transfusion must be same Rh (D) as recipient.

Question 8

What are the 5 ways to test for ABO blood group

*agglutination is visually apparent.

IgG antibody is most common naturally occurring one)

Answer 8

A. Detection of the specific ABO antigens in blood sample by

1) Adding commercial monoclonal reagents =IgM to RBCs which produce direct agglutination (bc larger than zeta potential of RBC).
(Tile method or measuring potency of agglutination in tube)

2)Automated gel card putting patient serum in gel capsule with specific antibody so that if it agglutinates its too dense to fall down into the gel, but individual RBC without agglutination will drop to the bottom (negative result)

B. Checking for presence of antibodies against ABO antigen in patient sample to infer type

3) Adding Anti human globulin (or other enzymes/albumin) which is a potentiator to help IgG antibodies for a specific ABO antigen to agglutinate in blood sample. (direct coombs)
4) Detection of free floating antibodies in recipient serum to RBC antigens in donor blood by adding anti human globulin to mix of both to see if there is antibody binding to the donor RBCs
5) Automated gel card for antibodies - RBCs put in with specific antigens tested against patients antibodies

Question 9

What are the 3 main causes of haemolytic disease of the foetus/newborn and what is the pathophysiology

Answer 9

• Presence of Anti RhD, anti-c and then anti Kell maternal IgG antibodies generated by a mother that is negative for those antigens

1. Sensitising event- exposure of fetal to maternal blood -
   eg. first birth, amniocentesis, termination, miscarriage
2. Leads to production of IgG antibody
3. Production is restimulated in second pregnancy and by third there is a strong antibody response crossing the placenta and attacks foetal red cells that have the antigen
4. May result in still birth/perinatal death, brain damage due to jaundice after birth

Question 10

How is haemolytic disease of newborn prevented and how is dosing decided

Answer 10

Anti-D immunoglobulin is given to RhD negative mother after

• birth, termination, amniocentesis of a RhD positive baby
  + routine antenatal prophylaxis in 3rd trim

These neutralise any RhD positive fetal antigens that may have entered the maternal circulation to prevent antibody forming.

Kliehauer test detects women with larger % of fetal RBC in maternal circulation so the right amount of standard dose can be given

Question 11

What is ABO haemolytic disease of newborn, treatment and prevalence

Answer 11

ABO incompatibility is common and significant haemolytic disease is rare - usually mild and transfusion rarely required

This is because AB antigens are only weakly expressed on fetus/newborn and AB antigens are widely distributed in placental tissue and absorb antibody before it reaches the foetus-