Lecture 6: Blood Group Serology Flashcards
Describe the genetic controls of blood groups:
- Protein determinants i.e Genes code for the antigenic determinant itself such as; Rh, Kelly, Duffy, Kidd systems
- Gylcolipid determinants i.e gene codes for the production of enzymes that add or remove carbohydrate or lipids; ABO, lewis body group
Whats the functional aspect of the duffy blood group system and why is it of clinical concern?
- 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
What is the mcleod phenotype?
Kx null phenotype associated with chronic granulomatous disease and acanthocytosis (this is caused by neighboring genes)
What does variation in blood groups represent?
Genetic drift, varies significantly within a population.
No apparent advantages, but represents clinical challenge’s for blood matching etc.
How do babies ABO groups vary?
Newborns have no ABO groups and these develop co-incidentally because of food/infections etc.
Why do naturally occurring red cell antibodies sometimes develop?
Typically cross reacting because of bacterial infection.
Usually related to lipid antigens (typically IgM+/-IgG)
Why do immune stimulated red cell antibodies occur?
Produced following exposure
- Transfusion
- Pregnancy
- Injection
Normally IgG in nature (Compared to naturally IgM, cross reacting)
Describe the structure of ABO blood groups:
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
Describe the ABO antigens present in each blood group:
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
What can inappropriate blood transfusions lead to?
Compliment activation which can cause:
- Intravascular heamolysis
- Renal failure
- DIC
Whats the universal donor and recipient?
Type O = Universal donor
Type AB = Universal recepient
What is the Rh blood group?
Rhesus factor, highly immunogenic, particularly Rh(D)
- Protein, only expressed on RBC
What are the genotypes for rhesus factor?
DD, Dd = RH +ive
dd = Rh -ive
What are the practical aspects of Rh and transfusions?
- 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.
How complex is the RHd system?
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.
What are the minor blood group systems?
400+ identified….
Mostly of theoretical interest.
Clinically important relating to:
- Hz of antigen in population
- Ability of Ab to destroy RBC
What are some minor blood groups systems?
- Kell
- Kidd
- Duffy
How are minor blood groups tested?
- Antigen-antibody agglutination
- Monoclonal antibodies (higher sensitivity and specificity)
What causes heamolytic disease of newborn?
- 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
What else can heamolytic disease of newborns cause?
Enlarged liver, spleen, anaemia
Unconjugated billirubin binds to brain and causes kernicterus
How can heamoyltic disease of newborn be prevented / reduced chances?
- Prophylactic Anti-D to D negative mums with D +ive babies
- Destroys fetal RBC in maternal blood before her immune system is activated
Does ABO heamolytic disease of the newborn occur often?
- 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.
