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haem > blood transfusion > Flashcards

blood transfusion Flashcards

1
Q

what does the clinical importance of a blood group system depend on?

A

the capacity of antibodies against the specific RBC antigens to cause haemolysis of the RBCs

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2
Q

What are the two classes of diseases/conditions that clinically significant antibodies against RBC antigens can cause?

A

HTRs and HDFN

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3
Q

What is HTR

A

haemolytic transfusion reactions

incompatible red cells are transfused - so the transfused RBCs have the antigen corresponding to antibodies in the patient’s plasma

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4
Q

what is HDFN

A

haemolytic disease of the foetus and newborn

the foetus has a different RBC antigen to the mother, and the mother has produced an antibody to that RBC antigen which has crossed the placenta.

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5
Q

What are the naturally occurring ABO antibodies?

A

anti-A and anti-B

antigens may be encountered in foods or micro-organisms

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6
Q

what class are ABO antibodies mostly

A

IgM antibodies

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7
Q

What type of haemolysis- caused reaction do the IgM antibodies cause?

A

acute HTRs through activation of the complement system

results in massive intravascular haemolysis

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8
Q

when are acquired antibodies formed?

A

as a result of active immunisation to non-self RBC antigens following exposure to RBCs eg from another person

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9
Q

are all alloantibodies clinically significant?

A

no

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10
Q

What class are acquired alloantibodies usually?

A

IgG

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11
Q

What can acquired alloantibodies cause?

A

mainly extravascular haemolysis resulting in delayed HTRs

IgG antibodies can cross the placenta and cause HDFN

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12
Q

what does the A gene code for?

A

an enzyme which adds N-acetyl galactosamine (GalNac) to the common H-antigen, making the A antigen

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13
Q

what does the B gene code for?

A

an enzyme which adds galactose (Gal) to common H antigen to form the B antigen

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14
Q

what does the O gene code for?

A

an enzyme which adds galactose (Gal) to common inactive enzyme

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15
Q

Why do IgG antibodies not usually cause HDFN despite being able to cross the placenta?

A
  • fetal red cells have poorly developed ABO antigens, they are unable to support the binding of the IgG antibodies
  • ABO antigens are found on numerous other cells- any IgG ABO antibodies which have crossed the placenta will bind to the other cells
  • maternal IgG anti-A or anti-B antibodies present at birth in a baby’s plasma will disappear within a few months when the baby develops their own IgM antibodies
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16
Q

universal red cell donor?

A

group O (no A or B antigens so no acute HTR despite patient’s antibodies)

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17
Q

universal plasma donor?

A

group AB (no antibodies so no HTR)

18
Q

inheritance pattern of D antigen

A

autosomal dominant

19
Q

How long after exposure does I take for anti-D antibodies to become apparent?

A

2 to 5 months

20
Q

what can anti-D antibodies cause?

A

delayed HTRs - extravascular, if RhD positive red cells are transfused- this results in anaemia, high bilirubin and therefore jaundice

HDFN (important) if a mother has IgG anti-D antibodies and the baby is RhD positive, the IgG antibodies can cross to the placenta which can lead to intra-uterine death or brain damage from high levels of bilirubin

21
Q

how do you prevent the formation of anti-D antibodies?

A

ensure RhD negative patients receive RhD negative red cells and platelet transfusions

in PREGANT WOMEN:
give them anti-D immunoglobulin! destroys any RhD positive foetal RBCs in the maternal circulation before the mother has time to create an immune response.

22
Q

Types of Pre-transfusion compatibility testing

A

ABO, RhD and antibody screen

collectively known as “group and screen”

23
Q

what’s the forward group in regards to ABO resting

A

when the patient’s RBCs are tested against reagent anti-ABO antibodies

interaction results in agglutination which can be seen

so agglutination w the anti reagent for a specific blood group means that it’s that blood group present

24
Q

what’s the reverse group in regards to ABO testing?

A

when the patient’s serum is mixed with reagent A and B RBCs

interaction results in agglutination

25
Q

what’s an antibody screen used for?

A

to detect the presence of any acquired alloantibodies

26
Q

what happens in an antibody screen

A

patient’s serum is tested against panels of RBCs which are known to express all of the clinically relevant RBC antigens

if there’s an interaction between an antibody in the patient’s serum and the antigen on the RBCs, agglutination will occur and antibody screen is positive

cannot be directly seen

27
Q

What is a cross match

A

when the patient’s plasma is tested against a sample of RBCs from the unit of red cells selected for a blood transfusion

28
Q

when does a cross match give a compatible result

A

when there is no agglutination

29
Q

what two types of tests are undertaken on blood donations?

A

group and screen tests
infection screening

30
Q

which group and screen tests are done on blood donations

A

ABO and RhD (all blood groups)

other Rh blood groups like C, c, E, e and K are also determined

sometimes other blood groups like Fya, Fyb, Jka, Jkb are tested for

tested also to ensure no strong clinically significant antibodies against RBCs are present in the plasma

31
Q

what infection screening occurs on blood donations?

A

HIV, Hep B C and E, HTLV, Syphilis

32
Q

What is apheresis?

A

The process of separating the particular components required from a blood donation

33
Q

How many units of RBCs can be collected from one blood donation?

A

1, sometimes 2 if apheresis is used

34
Q

How long is the shelf life of packed red cells?

A

35 days at 4 degrees C

35
Q

How many blood donations are needed for one unit of platelets ?

A

4, 1 if apheresis is used

36
Q

shelf life of platelets?

A

7days, 22 degrees C.

platelets require constant agitation to ensure they’re continuously oxygenated

37
Q

what is FFP

A

FFP contains all coagulation factors

38
Q

how many units of FFP are obtained from 1 whole blood donation?

A

1

39
Q

shelf life and storage of FFP

A

3 years, -25 degrees C, once thawed must be used within 24 hours, after being stored at 4 degrees C

40
Q

what’s cryoprecipitate?

A

it contains fibrinogen, factor 8, von willebrand factor and factor 13

41
Q

standard dose of cryoprecipitate for adults

A

2 units

haem (4 decks)

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