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Y2 MCD Haematology > haemostasis > Flashcards

haemostasis Flashcards

blood transfusion: list the major blood groups, explain their clinical importance, explain the screening of blood donors, list the blood components used clinically and recall the potential side effects of blood and plasma transfusions

1
Q

where is blood from and significance

A

human source (no synthetics yet), not risk free

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2
Q

why is blood used carefully

A

scarce resource (1 donor gives 1 pint every 4 months, and has shelf life of 5 weeks)

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3
Q

when is blood used and whose decision is it

A

balance between benefits and risk, so when no safer alternative is available; doctor’s decision and must prescribe

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4
Q

2 situations when no safer alternatives are not available to blood

A

if massive bleeding, if “plain fluids” are not sufficient; if anaemic, if iron/B12/folate are not appropriate

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5
Q

what is the most important of all blood groups in use for transfusion, and significance

A

ABO (cross match between donor and patient); should not die of ABO incompatible blood transfusion (human error still does)

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6
Q

physiology of ABO blood groups

A

A and B antigens on red cell formed by adding one or other sugar residue onto common glycoprotein and fucose stem on red cell membrane; group O has neither A or B sugars (stem only), group AB has both A and B sugars

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7
Q

how are ABO antigens determined

A

by corresponding genes

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8
Q

what does A gene code for

A

enzyme which N-acetyl galactosamine to common glycoprotein and fucose stem

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9
Q

what does B gene code for

A

enzyme which adds galactose to common glycoprotein and fucose stem

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10
Q

what are A and B genes

A

codominant (e.g. for blood group A, could be AA or AO)

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11
Q

what is O gene

A

recessive (e.g. for blood group A, could be AA or AO)

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12
Q

what antibodies exist in humans concerning red cells

A

IgM, which are against any antigen not present on own red cells

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13
Q

what type of antibody is IgM, and what it activates

A

naturally occurring (nearly from birth), and is “complete” antibody so fully activates complement cascade to cause haemolysis of red cells (forms membrane attack complex)

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14
Q

when is antibody/antigen interaction often fatal

A

in patient who has received an ABO incompatible transfusion, where patient has corresonding antibody -> Hb (toxic to kidney), bilirubin (jaundice), cytokine storm (hypotension and shock)

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15
Q

what do IgM antibodies do to corresponding antigens (e.g. when anti-A antibodies from group B patient are added to group of A cells), and what does it show

A

cause agglutination, showing cells are incompatible

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16
Q

what blood group has no antigens on red cells, and consequently has 2 sets of anti-antibodies in blood

A

O (agglutinate to any transfusion except O; red cell blood transfusion can be given to anyone)

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17
Q

what blood group has 2 antigens on red cells, and consequently has no anti-antibodies in blood

A

AB (so safe with any blood transfusion)

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18
Q

how is ABO group known

A

test patient blood sample (plasma and cells) with known anti-A and anti-B reagents and see if it clumps;

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19
Q

how is a cross match conducted to ensure compatibility

A

donor unit of same group selected, and patient’s serum mixed with donor red cells (should not react - if it agglutinates, it is incompatible)

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20
Q

of the RH antigen groups, what is the most important and why

A

RhD, as next most immunogenic

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21
Q

RhD positive vs RhD negative

A

RhD (DD or Dd) positive is if you have antigen, RhD negative (dd) if not

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22
Q

genes for RhD groups

A

D codes for D antigen on red cell membrane, d codes for no antigen and is recessive

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23
Q

naming combination of ABO and RhD groups

A

usually shortened, e.g. O positive means ABO group O and RH D positive

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24
Q

when can RhD negative people make anti-D antibodies

A

after exposed to RhD antigen, either by transfusion of RhD positive blood, or in women if pregnant with RhD positive foetus

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25
Q

what type of antibodies are anti-D antibodies

A

IgG

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26
Q

anti-D antibodies implications for future transfusions

A

must have RhD negative blood, otherwise anti-D would react with RhD positive blood, causing delayed (5-10 days as IgG attach to red cells but can’t activate complement system as quickly - only when macrophages in spleen detect) haemolytic transfusion reaction (anaemia, high bilirubin, janudice etc.)

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27
Q

anti-D antibodies implications for haemolytic disease of newborn (HDN)

A

if RhD negative mother has anti-D and in next pregnancy, foetus is RhD positive, mother’s IgG anti-D antibodies can cross placenta, causing haemolysis of foetal red cells (if severe, hydrops fetalis as foetus as anaemic so heart failure; death by brain damage due to bilirubin staining); prevent sensitisation by giving anti-D injections during delivery so doesn’t mount anti-D response against foetus

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28
Q

RhD group importance

A

avoid Rh D negative patients making anti-D

29
Q

how do you avoid Rh D negative patients making anti-D

A

transfuse blood of same RhD group (no harm to give RhD neg to a positive patient, just wasteful); O neg used as emergency when blood group not known

30
Q

other Rh antigen red cell groups which are not routinely matched

A

C, c, E, e, Kell, Duffy, Kidd

31
Q

once antibodies have formed to another antigen red cell group following transfusion, what must be done

A

use corresponding antigen negative blood, or else risk delayed haemolytic reaction

32
Q

how is it known if a patient will need antigen negative blood

A

test patient’s blood sample for red cell antibodies before each transfusion episode (using donor screening (and cross match) for ABO and RhD, then an “antibody screen” of plasma)

33
Q

what is 1 unit of blood collected into

A

bag containing anticoagulant

34
Q

why is whole blood not routinely given to patients (2 things)

A

more efficient (less waste as patients don’t need all components), some componenets degrade quickly if stored as whole blood

35
Q

how are red cells concentrated and what does this avoid

A

plasma removed, avoiding fluid overloading patients

36
Q

how are blood components separated

A

split one unit of blood by centrifuging whole bag (red cells bottom, platelets (and white cells) middle, plasma top), then squeeze each layer into satellite bags and cut free with heat seal (closed system to prevent bacteria)

37
Q

3 ways plasma is stored

A

FFP (fresh frozen plasma - contains all coagulation factors), cryoprecipitate (rich source of FVIII and fibrinogen), plasma for fractionation (not UK)

38
Q

what is plasma fractionated into

A

albumin, FVIII, FIX, immunoglobulins, anti-D etc.

39
Q

shelf life and storage of red cells

A

1 unit from 1 donor stored as packed cells (fluid plasma removed), with a shelf life of 5 weeks and stored at 4 degrees celsius in fridge

40
Q

how are red cells given

A

through a blood giving set which has a filter to remove clump/debris

41
Q

when would you need frozen red cells (national frozen bank), and disadvantage

A

only for rare groups/antibodies; poor recovery on thawing (add glycerol to prevent ice crystals)

42
Q

shelf life and storage of FFP (fresh frozen plasma)

A

1 unit from 1 donor (300ml) stored at -30 degrees celsius (frozen within 6 hours of donation to preserve coagulation factors), with a shelf life of 2-3 years

43
Q

how is FFP given and dose

A

must thaw approx 20-30 minutes before use (at room temperature, as if too hot, proteins cook); give ASAP (within 1 hour) otherwise coagulation factors degenerate at room temperature; dose 12-15ml/kg (usually 3 units)

44
Q

what must be known to give FFP and why

A

blood group (no cross match just choose same group, as contains ABO antibodies which could cause some haemolysis)

45
Q

when is FFP given (3 occasions)

A

if bleeding (or about to in surgery) and abnormal coagulation test results (PT, APTT), reversal of warfarin (anticoagulant), other conditions (not just to replace volume or fluid loss - use saline etc.)

46
Q

what must be done after giving FFP if bleeding and abnormal coagulation test results (PT, APTT)

A

monitor response (clinically and by coagulation tests)

47
Q

example of when using FFP to reverse effects of warfarin (anticoagulant inhibiting FII, FVII, FIX and FX)

A

for urgent surgery if PCC (concentrate of FII, FVII, FIX and FX) not available

48
Q

what is cryoprecipitate from

A

from frozen plasma thawed at 4-8 degrees celsius overnight residue remains

49
Q

what does cryoprecipitate contain

A

fibrinogen and FVIII

50
Q

shelf life and storage of cryoprecipitate

A

same as FFP, store at -30 degrees celsius for 2 years

51
Q

standard dose of cryoprecipitate

A

from 10 donors, with 5 in a pack

52
Q

2 times when you would use cryoprecipitate

A

if massive bleeding and very low fibrinogen, rarely hypofibringaemia

53
Q

standard adult dose of platelets

A

1 pool from 4 donors, or from 1 donor by apheresis (cell separator machine)

54
Q

storage and shelf life of platelets

A

store at room temperature (22 degrees celsius) and constantly agitate to prevent clumping; shelf life of 5-7 days (risk of bacterial infection) so run out first

55
Q

what must be known to transfuse platelets

A

blood group (no cross match as platelets have low levels of ABO antigens, so wrong group would cause platelets to be destroyed more quickly, or haemolysis of some of patient’s red cells; can also cause RhD sensitisation as some red cell contamination)

56
Q

4 times when you would use platelets

A

haematology patients with bone marrow failure causing low platelets, massive bleeding or acute disseminated intravascular coagulation, if very low platelets and patients needs surgery, if for cardiac bypass and patient on anti-platelet drugs

57
Q

large pool of fractionated plasma products: what are FVIII and FIX used for

A

haemophilia A and B respectively (males), FVIII for von Willebrand’s disease

58
Q

large pool of fractionated plasma products: how are FVIII and FIX treated and why

A

heat treated for viral inactivation; recombinant FVIII or FIX alternatives increasingly used but expensive

59
Q

large pool of fractionated plasma products: IM

A

specific antibodies collected to treat tetanus, anti-D or rabies; normal globulin - broad mix in population

60
Q

large pool of fractionated plasma products: IVIg

A

pre-op in patients with ITP or AIHA

61
Q

large pool of fractionated plasma products: when is albumin used (4.5% and 20%)

A

4.5% useful in burns and plasma exchanges, 20% (salt poor) used for certain severe liver and kidney conditions only

62
Q

how are donors screened

A

by testing for some infections, by questioning for risk behaviour to exclude them, by questioning to exclude donors posing risk to themselves (e.g. heart problems)

63
Q

examples of infections blood must be tested for

A

Hep B, C and E, HIV, HTLV, syphilis, CMV, other viruses; most by antibody testing or PCR

64
Q

why cannot donors rely on testing

A

window period of infections so test will not show positive, so must exclude high risk donors (e.g. IV drug injecting; if risk in group is >1% would double transmission of disease) and use voluntary, unpaid donors

65
Q

what disease can be transmitted by blood transfusion

A

prion disease vCJD

66
Q

2 precautions to avoid prion disease vCJD transmission

A

all plasma pooled to make fractionated products now obtained from USA (in UK plasma, some used for FFP and rest thrown away), all blood components have white cells filtered out (leucodepleted) as essential for uptake of vCJD prion into brain to cause disease

67
Q

what does the fingerprick test of the donor estimate

A

Hb (not iron)

68
Q

if O positive and AB positive parents, what ABO groups can children not be

A

O positive or AB positive

69
Q

if patient is B positive, which blood could kill them

A

A positive and negative

Y2 MCD Haematology (20 decks)

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