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Immunity Week 3 > ICL 12: Blood Transfusion > Flashcards

ICL 12: Blood Transfusion Flashcards

1
Q

what are the two most significant blood groups for clinical consideration?

A

ABO and RhD groups

they must be tested prior to blood transfusion for safety

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2
Q

what is a blood group antigen?

A

portions of molecules on either oligosaccharides or polypeptides that are recognized by antibodies

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3
Q

what is a blood group system?

A

grouping of RBC antigens based on genetic, serologic and/or biochemical relationships

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4
Q

in what scenario would you try to match RhD?

A

RhD is only expressed on RBCs so we ignore them for organ transplants

you only need to match ABO for an organ transplant

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5
Q

what is the most important blood group system?

A

ABO blood groups

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6
Q

why are ABO blood groups the most important?

A

because of naturally-occurring antibodies which are present opposite to the antigens expressed on red blood cells

these antibodies have high titers and high avidity to their antigens

Ab are mostly IgM so they’re capable of complement activation through MAC

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7
Q

where are A and B antigens present?

A

RBCs

also present on other cells like endothelial cells

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8
Q

how are ABO antigens formed?

A

the ABO genes encode for specific glycosyltransferases which add sugars sequentially to sites on short chains of sugars

polysaccharides are not directly encoded by genes but the enzymes that regulate the construction of polysaccharides that are responsible for the type of blood group that you have are!

so the gene codes for a specific glycosyltransferase that will attach a certain sugar that makes you blood type A, B, or O – it just depends which glycosyltransferase is active

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9
Q

what chromosome are the ABO genes on?

A

chromosome 9

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10
Q

what does the A allele of the ABO locus code for?

A

a glycosyl transferase that bonds alpha-N-acetylgalactosamine to the D-galactose end of the H antigen producing A antigen

this gives you blood type A!

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11
Q

what does the B allele of the ABO locus code for?

A

a glycosyl transferase that bonds alpha-D-galactose end to the H antigen producing a B antigen

this gives you blood group B!

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12
Q

what does the O allele of the ABO locus code for?

A

in the O allele, exon 6 in glycosyl-transferase gene lacks a guanine nucleotide which results in loss of enzymatic activity and the H antigen remains unchanged

so when you have a mutation in the transferase there’s no sugar groups added and you get blood type O!

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13
Q

can two parents who are phenotypically A blood group have an O blood type child?

A

yeah if both of their genotype is AO

25% chance

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14
Q

what is forward typing?

A

it determines the antigen on the RBC! aka if the RBCs are A, B, or O

if you centrifuge a blood sample, you take the RBCs and put them in two tubes

in one tube you put anti-A antibodies and int the other you put anti-B antibodies

if there is agglutination in the anti-A tube, it means that it’s blood type A

if there is agglutination in the anti-B tube it means that it’s blood type B

if both tubes are positive then it means it’s blood type AB

if neither tube is positive then it’s blood type O

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15
Q

what is reverse typing?

A

determines the antibody in the plasma!

you take a patients serum and expose it to RBC of a known blood type – the serum is where the antibodies are

so if the plasma is from an A blood type, it will have antibodies against B and vice versa

if the plasma is from an AB patient, it won’t have any antibodies

if the plasma is from an O patient, there will antibodies against both A and B

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16
Q

where are antibodies found?

A

they occur naturally in plasma

they react not only with red blood cells but also with endothelial cells and other cells

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17
Q

what kinds of ABO antibodies are found in the blood?

A

antibodies found in the blood are opposite to the antigens found on the RBCs!

ex. a person with A blood type will have anti-B antibodies

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18
Q

what kind of antibodies will an A blood type have?

A

anti-B antibodies

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19
Q

what kind of antibodies will an B blood type have?

A

anti-A antibodies

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20
Q

what kind of antibodies will an AB blood type have?

A

no antibodies

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21
Q

what kind of antibodies will an O blood type have?

A

anti-A and anti-B antibodies

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22
Q

what is the most immunogenic of the blood group systems?

A

RhD

Rh is a protein which is more immunogenic than ABO which are sugars!

this is why we test for RhD antigen because it is the most immunogenic and match RhD positive and RhD negative blood for transfusion

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23
Q

do we have Rh antibodies?

A

RhD antibodies must be induced because they are not naturally expressed!!

only when we are exposed to RhD+ antigen (like in a blood transfusion) would be produce antibodies against it

the best example is pregnancy – if a woman is RhD- it means she’s never been exposed to the RhD antigen

but if her baby is RhD+ she’ll get exposed to RhD+ and start making antibodies against it

so then during her second pregnancy she would be sensitized to RhD and have antibodies against it which could target the RBCs of her fetus and kill it

24
Q

can two RhD+ parents have an RhD- child?

A

yes, if they are heterozygous = RHD/RHX

there is a 25% chance the kid could be RHX/RHX and end up RhD-

25
Q

how do the anti-Rh antibodies work?

A

they are IgG antibodies

they don’t bind complement!

26
Q

what are the characteristics of the ABO system?

A
  1. based on carbohydrates!
  2. genes code for enzymes
  3. mostly IgM antibodies that bind compelement
  4. naturally occurring; preformed antibodies from the gut we think
  5. antigens widely distributed
27
Q

what are the characteristics of the Rh system?

A
  1. based on polypeptides! aka proteins!
  2. genes directly code for antigen
  3. IgG antibodies which rarely bind complement; can cross placenta!!
  4. antibodies formed as result of exposure to blood
  5. found on only RBCs!
28
Q

what type of antibodies are in the ABO system?

A

IgM

sometimes it’s IgG especially in group O which can cross the placenta

29
Q

what type of antibodies are in the Rh system?

A

IgG

30
Q

on what cells is Rh found?

A

RBC only!

31
Q

what does HDFN stand for?

A

hemolytic disease of the fetus and newborn

32
Q

what is HDFN?

A

90% of women are RhD+ but some women are RhD-

RhD- mother will make antibodies against fetus’s RhD+ RBCs but the first pregnancy is usually fine because the baby will be born before any significant amount of antibody is made

generally affects the 2nd pregnancy!

so during the second pregnancy, the IgG anti-RhD antibodies can cross into the placenta and tag the fetus’s RBC for destruction = anemia

33
Q

how do you treat HDFN?

A

RhIg given twice – once at 28 weeks and again during delivery and then again with future pregnancies

anti-D immunoglobulin neutralises any RhD positive antigens that may have entered the mother’s blood during pregnancy – if the antigens have been neutralised, the mother’s blood won’t produce antibodies

34
Q

how are patients properly identified for blood transfusions?

A

TWO identifiers

their name and their ID number

35
Q

what do you do during a pretransfusion workup?

A

review their past medical records to see if they have any clinically significant antibodies

36
Q

what do we not test for before a blood transfusion?

A

we don’t test for or try to match HLA because it’s impossible

consequently, blood transfusions are inducing an alloimmune response to HLA….

this will make any future BM matches a lot harder because patients are developing new memory T cells and circulating antibodies

37
Q

what two tests do you have to do before a transfusion?

A
  1. ABO/Rh typing
  2. serum screening for clinically significant, unexpected antibodies

serum screening is necessary to protect from any alloantibodies present in a patient, especially when previously sensitized by previous blood transfusions or pregnancies in women

38
Q

what are the two tests that you can do to test for antibodies in someone’s blood before a transfusion?

A
  1. direct agglutination test

2. indirect agglutination test –> direct antiglobulin test and indirect antiglobulin test

39
Q

how does the direct agglutination test work?

A

mix the recipients serum with donors RBCs

if there are any IgM antibodies in the plasma, they will bind to the RBCs and cause them to clump – you can see this with the naked eye!

40
Q

how does the direct antiglobulin test work?

A

it’s the same as the direct agglutination test but you add anti-human globulin antibodies

so you take the serum of the recipient and the RBCs of the donor and then adding AHG to enhance the reactivity of the antibodies in the plasma

the antibodies are already present in the serum and they’re binding the RBCs but you can’t visibly see the agglutination so you add AHG to enhance the binding

you do this assay if someone has had a prior transfusion because this would cause their antibodies to have been diluted

41
Q

how does an indirect antiglobulin test work?

A

you do this test to identify which antigen is present (RhD, RhC or RhE)

you take monoclonal antibodies that we know for a fact recognize RhC for example – then we add these monoclonal antibodies to RBCs knowing that they should recognize RhC – and on top of this we also add AHG to allow for very visible agglutination

if you see agglutination it tells you which antigen is present!

42
Q

what are the characteristics of IgM?

A

pentamer = has 10 binding sites

used in direct agglutination test!

activates complement

43
Q

what are the characteristics of IgG?

A

monomer

usually used in indirect agglutination!

44
Q

what is a type and screen test?

A

the patient’s blood is ABO/Rh typed and screened for alloantibodies

this is reserved for surgeries that rarely require transfusion

if there’s no alloantibody identified then the blood bank will ensure blood is available

if there is an alloantibody present, then antigen negative units are identified

45
Q

what is a type and crossmatch?

A

the patient’s blood is ABO/Rh typed and screened for alloantibodies

ALSO, the patients plasma/serum is tested against donor RBCs to determine compatibility

46
Q

what are the types of crossmatch?

A
  1. immediate spin crossmatch
  2. antiglobulin crossmatch
  3. computer crossmatch
47
Q

what is immediate spine crossmatch?

A

a patient’s serum is tested against donor’s RBCs

this is the final check on ABO compatibility done at bedside before a blood transfusion just to confirm there isn’t a mixup

48
Q

what is the anti globulin crossmatch?

A

this is done for a patient who has a current or history of RBC alloantibodies!!

it’s the patients serum + donor cells + antihuman globulin reagent

49
Q

what criteria has to match when you’re giving a platelet transfusion?

A

preferably, the platelets are compatible with the recipients RBCs

but in an emergency and since platelets are in such high need, sometimes ABO blood group is ignored and this just means patients will get sensitized to alloantigens

50
Q

what blood types is type A compatible with?

A

A and O

51
Q

what blood types is type B compatible with?

A

B and O

52
Q

what blood types is type AB compatible with?

A

A, B, AB, and O

53
Q

what blood types is type O compatible with?

A

O

54
Q

what blood type is a universal RBC donor?

A

O-

O doesn’t have any antibodies and RhD- means it doesn’t have any antigens against Rh either

so it’s a universal donor since it doesn’t have antibodies against anything

55
Q

what blood type is a universal plasma donor?

A

AB

it doesn’t have any antibodies

56
Q

what blood type is a universal RBC recipient?

A

AB+

it’s been sensitized to everything

57
Q

what blood type is a universal plasma recipient?

A

O

Immunity Week 3 (14 decks)

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