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Y3 immunology and haematology > blood transfusion > Flashcards

blood transfusion Flashcards

1
Q

why do we transfuse blood

A

low levels of blood

  • bleeding
  • failure of production
  • XS rate of destruction
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2
Q

how do different blood groups arise

A

from surface antigens on red blood cells (mic of proteins and sugars)

surface antigens can provoke antibodies and therefore immune response

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3
Q

what does the ABO gene encode for

A

glycosyltransferase

glycans added to proteins or lipids on red cells

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4
Q

what do A and B genes code for

A

transferase enzymes

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5
Q

what are the A and B antigens

A

A - N-acetyl-galactosamine

B - galactose

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6
Q

what is the O gene

A

non-functional allele

A and B are co-dominant and O is recessive

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7
Q

antibodies against different blood groups

A

blood group A = antibodies against B
blood group B = antibodies against A
blood group O = antibodies against A and B
blood group AB = NO antibodies against A and B

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8
Q

prevalence of different blood groups in UK

A

A 42%
B 9%
AB 3%
O 46%

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9
Q

how do we encounter the ABO entigens

A

encoded by many bacteria in the bowels
- anti-A/B naturally occurring

because they are sugars you form an IgM

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10
Q

thermal range of IgM antibodies

A

most only react to cold temps e.g. 20 degrees

ABO antigens are particularly strong and thermal range often goes up to 37 degrees - why there are such catastrophic reactions irl

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11
Q

red cell donor/recipient compatibility

A 
O. = universal donor 
AB = universal recipient

x combinations can cause a severe ABO reaction and you should never transfuse these combinations

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12
Q

red cell vs FFP donor/recipient compatibility

A

plasma contains antibodies

e.g. B donor will have anti-A in their plasma so can’t donate to A patient

reactions to plasma are usually much less severe than red cells

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13
Q

RhD blood group system

A

protein antigen which crosses the membrane

very immunogenic protein - if you are an RhD individual and you are exposed to all the epitopes in the RhD gene, you are highly likely to make an antibody against it (?)

varies between racial groups

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14
Q

RhD nomenclature

A

DD - +ve for RhD gene

dd - -ve

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15
Q

anti RhD

A

RhD -ve individuals can make anti-D if exposed to RhD +ve cells (transfusion or pregnancy)

anti-D can cause transfusion reactions or haemolytic disease of the newborn

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16
Q

screening in blood donors

A

medical hx, prev transfusion

sex, age, travel, tattoos etc

tested for ABO and Rh blood groups

screened for hepB/C/E, HIV, syphilis

variably screened for: HTLV1, malaria, west nile virus, zika virus (depending on travel hx etc)

17
Q

indications for red cell transfusion

A
  • correct severe acute anaemia, which might otherwise cause organ damage
  • improve QOL in pt w/ otherwise uncorrectable anaemia
  • prepare a pt for surgery or speed up recovery
  • reverse damage caused by pts own red cells e.g. sickle cell disease
18
Q

red cell transfusion

A

red cells stored at 4 degrees

transfuse over 2-4hrs

1 unit increments ~5g/L

19
Q

platelet transfusion

A

1 dose platelets = 4 pooled/1 apheresis donor

increments ~30.10^9/L

stored at ~22C, shelf life 7 days

transfuse over 20-30 mins

20
Q

indications for platelet transfusion

A

massive haemorrhage - keep platelet count above 75.10^9/L

BONE MARROW FAILURE (platelet count < 10-15.10^9/L OR <20.10^9/L if additional risk e.g. sepsis)

prophylaxis for surgery - minor procedures 50.10^9/L, more major surgery 80.10^9/L, CNS/eye surgery 100.10^9/L

CP bypass - use only if bleeding

21
Q

fresh frozen plasma

A

1 unit from 1 unit of blood

stored frozen, allow 30 mins to thaw

lab test - PT and APTT

22
Q

indications for fresh frozen plasma

A

massive haemorrhage (use in 1:1 ratio)

DIC w/ bleeding

prophylactic - pts expected to bleed e.g. liver failure

23
Q

cryoprecipitate

A

1-2 pools if fib <1.0g/dl (1.5g/dl)

stored frozen, allow 20 mins to thaw

lab test: fibrinogen

used when you want to give lots of fibrinogen to someone and you haven’t got much intravascular volume to give it in

24
Q

how to choose compatible blood

A

blood sample (EDTA)

2 sample policy

group and screen/save

cross matching

25
Q

what is group and screening

A

ABO and RhD type

checked against historical records for any discrepancy

screen for allo-antibodies in serum

26
Q

Coombs test

A

trying to detect the antibody on the surface of red cells

can pick up IgG on the surface of red cells by using anti-human globulin

27
Q

Coombs test: direct vs indirect

A

direct:
- AI haemolytic anaemia
- passive anti-D
- haemolytic transfusion reactions

indirect:
- cross matching

e.g. pt w/ AI haeomolytic anaemia, send for direct Coombs test, +ve = shows antibody on the surface of the red cell

28
Q

what is an indirect Coombs test

A

adding an external antibody to see if it binds the red cells which you then cross link

29
Q

allo-antibody screening

A

~1% of pop have antibodies

usually due to previous transfusion or pregnancy

10% of transfusion pts have had one before

30
Q

clinical significance of antibodies reactive at 37degrees

A

> 21 blood group systems: ABO, Rh, Kell, Duffy, MN, P

31
Q

development of maternal anti-D antibodies (sensitisation)

A

mothers can develop antibodies against antigens carried by their babies

~15% of mothers are RhD- and if the father is RhD+ they are at risk of developing the disease

red cells leak across the placenta (pregnancy/birth) - mother forms antibodies (IgG)

IgG can cross the placenta in subsequent pregnancies and cause alloimmune haemolysis in the baby

baby becomes profoundly anaemia, can develop cardiac failure and die

I

32
Q

haemolytic disease of the newborn

A

RhD most immunogenic (also c, K; other Rh antigens (JKA, ABO) less immunogenic)

+ve DAT at birth, anaemia, jaundice (profound haemolysis)

brain damage

33
Q

how to prevent HDN

A

give anti-D to RhD- mother

~28wks

RhD- w/ RhD+ baby should be given further anti-D at birth to prevent problems in future pregnancies

also given if any form of trauma during pregnancy (sensitising events)

34
Q

treatment of HDN

A

careful monitoring:

  • antibody titres
  • doppler US
  • intrauterine transfusions
35
Q

what is NAIT

A

neonatal alloimmune thrombocytopenia

similar process to HDN but for platelets

36
Q

cellular therapies

A

leucapheresis

  • stem cells for transplantation
  • lymphocytes for immunotherapy, CAR-T cells

other banks: bone, milk, tendons, heart valves, faecal; islet cells, mesenchymal stem cells

gene therapies

Y3 immunology and haematology (20 decks)

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