Lecture 6: Blood Group Serology

Question 1

Describe the genetic controls of blood groups:

Answer 1

1. Protein determinants i.e Genes code for the antigenic determinant itself such as; Rh, Kelly, Duffy, Kidd systems
2. Gylcolipid determinants i.e gene codes for the production of enzymes that add or remove carbohydrate or lipids; ABO, lewis body group

Question 2

Whats the functional aspect of the duffy blood group system and why is it of clinical concern?

Answer 2

• Acts as an entry point for the malarial parasite

- Fya-Fyb phenotype rare in caucasians but 40% of africans and is the cause of malarial resistance

Question 3

What is the mcleod phenotype?

Answer 3

Kx null phenotype associated with chronic granulomatous disease and acanthocytosis (this is caused by neighboring genes)

Question 4

What does variation in blood groups represent?

Answer 4

Genetic drift, varies significantly within a population.

No apparent advantages, but represents clinical challenge’s for blood matching etc.

Question 5

How do babies ABO groups vary?

Answer 5

Newborns have no ABO groups and these develop co-incidentally because of food/infections etc.

Question 6

Why do naturally occurring red cell antibodies sometimes develop?

Answer 6

Typically cross reacting because of bacterial infection.

Usually related to lipid antigens (typically IgM+/-IgG)

Question 7

Why do immune stimulated red cell antibodies occur?

Answer 7

Produced following exposure

• Transfusion
• Pregnancy
• Injection

Normally IgG in nature (Compared to naturally IgM, cross reacting)

Question 8

Describe the structure of ABO blood groups:

Answer 8

Composed of:

• H-antigen + N-acetylgalactosamine = A-antigen
• H-antigen + galactose = B-antigen
• H-antigen + nil = O blood group

I.e terminal sugar determines antigen

Question 9

Describe the ABO antigens present in each blood group:

Answer 9

OO = O-type = Anti-A and Anti-B
AA, AO = A type = Anti-B
BB, BO = B type = Anti-A
AB = AB type = Nil

These antibodies develop between 3-6 months of age

Question 10

What can inappropriate blood transfusions lead to?

Answer 10

Compliment activation which can cause:

• Intravascular heamolysis
• Renal failure
• DIC

Question 11

Whats the universal donor and recipient?

Answer 11

Type O = Universal donor

Type AB = Universal recepient

Question 12

What is the Rh blood group?

Answer 12

Rhesus factor, highly immunogenic, particularly Rh(D)

• Protein, only expressed on RBC

Question 13

What are the genotypes for rhesus factor?

Answer 13

DD, Dd = RH +ive

dd = Rh -ive

Question 14

What are the practical aspects of Rh and transfusions?

Answer 14

• Rh -ive if transfused will produce anti-Rh(d) 90% of time.
• Anti-Rh(d) is IgG that doesnt bind compliment, RBC destruction is extravascular
• Anti-D is most common cause of heamolytic disease in newborn

Never give RhD +ive blood to Rh(d) -ive female of child bearing age.

Question 15

How complex is the RHd system?

Answer 15

Consists of 3 genetically linked alleles

• C & c
• D & d
• E & e

But they behave as a single identity i.e CDE or CdE

But only really relevant in donor situations or family studies.

Question 16

What are the minor blood group systems?

Answer 16

400+ identified….

Mostly of theoretical interest.

Clinically important relating to:

• Hz of antigen in population
• Ability of Ab to destroy RBC

Question 17

What are some minor blood groups systems?

Answer 17

• Kell
• Kidd
• Duffy

Question 18

How are minor blood groups tested?

Answer 18

• Antigen-antibody agglutination

- Monoclonal antibodies (higher sensitivity and specificity)

Question 19

What causes heamolytic disease of newborn?

Answer 19

• Occurs when maternal antibody crosses placenta resulting in destruction of feotal RBC
• IgG antibodies
• Anti-D primarily, followed by Anti-C and Anti-kell
• Hz reduced by by introduction of immunoprophylaxis

Question 20

What else can heamolytic disease of newborns cause?

Answer 20

Enlarged liver, spleen, anaemia

Unconjugated billirubin binds to brain and causes kernicterus

Question 21

How can heamoyltic disease of newborn be prevented / reduced chances?

Answer 21

• Prophylactic Anti-D to D negative mums with D +ive babies

- Destroys fetal RBC in maternal blood before her immune system is activated

Question 22

Does ABO heamolytic disease of the newborn occur often?

Answer 22

• ABO incompatibility is common, but significant heamolytic disease is rare because AB antigens are weakly expressed by newborn and AB antigens widely expressed in placental and prevent AB antigens from entering the maternal circulation.