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Haematology > The Blood Transfusion Lab > Flashcards

The Blood Transfusion Lab Flashcards

1
Q

What are antigens?

A

Antigens are part of the surface of cells

All blood cells have antigens

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2
Q

What are antibodies?

A

Antibodies are protein molecules –immunoglobulins (Ig)

Usually of immunoglobulin classes: IgG and IgM

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3
Q

Where are antibodies found?

A

Found in the plasma

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4
Q

How are antibodies produced?

A

Produced by the immune system following exposure to a foreign antigen

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5
Q

What causes reactions to blood transfusion?

A

Reactions to blood usually occurs when the antibody in the plasma reacts with an antigen on the cells

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6
Q

How many blood groups are there?

A

There are 26 known blood group systems - ABO and Rh are clinically most important

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7
Q

Why do patients ‘reject’ transufused blood?

A

Antigens in transfused blood can stimulate a patient to produce an antibody but only if the patient lacks the antigen themselves

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8
Q

How often are antibodies produced in a transfused patient?

A

The frequency of antibody production is very low but increases the more transfusions that are given

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9
Q

What procedures stimulate antibody production?

A
  • Blood transfusion
  • Pregnancy
    Environmental factors
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10
Q

How does blood transfusion stimulate antibody production?

A

blood carrying antigens foreign to the patient

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11
Q

How can pregnancy stimulate antibody formation?

A

Fetal antigen entering maternal circulation during pregnancy or at birth

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12
Q

Describe how environmental factors contribute to antibody production

A

i.e. naturally acquired e.g. anti-A and anti-B

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13
Q

Outline an antigen-antibody reaction in vivo

A

in vivo (in the body) leads to destruction of cell either:

Directly (intravascular)
- cell breaks up in blood stream

Indirectly (extravascular)
- liver and spleen remove antibody coated cells

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14
Q

Describe an antigen-antibody reaction in vitro

A

In vitro (in the laboratory) reactions are normally agglutination tests

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15
Q

What is agglutination?

A

Agglutination is the clumping together of red cells into visible agglutinates by antigen-antibody reactions

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16
Q

What causes agglutination?

A

Agglutination results from antibody cross-linking with the antigens

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17
Q

What is the significance of agglutination tests?

A

As the antigen-antibody reaction is specific, agglutination can identify:-

  • Presence of red cell antigen i.e. blood grouping
  • Presence of antibody in plasma i.e. antibody screening /
    identification
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18
Q

What are common blood groups?

A

A and B antigens very common (55% UK)

Anti-A, anti-B or anti-A,B antibodies very common (97% UK)

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19
Q

What is a common error of transfusion in emergencies

A

High risk of A or B cells being transfused into someone with the antibody in a random situation

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20
Q

WHat is the effect of ABO transfusion?

A

ABO antibodies can activate complement causing INTRAVASCULAR HAEMOLYSIS

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21
Q

What is a common consequence of ABO transfusion error

A

(Almost) all serious / fatal transfusion reactions caused by technical / clerical error are due to ABO incompatibility

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22
Q

Outline the genetics of a patient with blood type A

A

Phenotype: A
RBC Antigen: A
Genotype: AA or AO
RBC Antibody: B

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23
Q

Describe the genetics of patients with Blood type B

A

Phenotype: B
RBC Antigen: B
Genotype: BB or BO
RBC Antibody: A

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24
Q

Outline genetics of Blood type O patients

A

Phenotype: O
RBC Antigen: none
Genotype: OO
RBC Antibody: A and B

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25
Q

Describe the genetics of patients with blood type AB

A

Phenotype: AB
RBC Antigen: A and B
Genotype: AB
RBC Antibody: none

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26
Q

How do we determine a blood type?

A

The patient’s red cells and plasma are both tested

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27
Q

Describe a blood grouping test done on blood

A

Test patient’s red cells with anti-A, anti-B and anti-D

  • agglutination = particular antigen on red cells
  • no agglutination = antigen is absent
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28
Q

Outline how plasma is tested for blood type

A

Test patient’s plasma with A cells and B cells

  • agglutination shows that a particular antibody in plasma / serum
  • no agglutination shows the antibody is absent
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29
Q

Outline blood compatibility for O blood group people

A

Can only receive blood from Group O

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30
Q

What blood donor groups are compatible for A type blood?

A

Can receive blood from other A types or O type blood

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31
Q

Who can Blood type B patients receive blood from?

A

Can receive blood from other B types or O type blood

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32
Q

Which blood groups are compatible fro AB patients?

A

AB patients can receive blood from O, A, B and AB blood type donors

33
Q

Describe the Rh grouping system

A

50+ antigens:
Most important antigen is called D

People with D antigen are D positive (85% of UK)

People who do not produce any D antigen are D negative (15%)

The other 4 main antigens are known as C, c, E and e

34
Q

How is Rh(d) testing carried out?

A

Must be tested in duplicate (or tested each time and compared to historical result)

35
Q

How are Rh(D) test result classified?

A

Patient / Donor classified as D pos or D neg

36
Q

How significant are Rh antibodies?

A

Rh antibodies are clinically significant, Second only to ABO

37
Q

How does Rh(D) react in transfusion?

A

D antigen is very immunogenic and anti-D is easily stimulated - PREVENTION!

All Rh antibodies are capable of causing severe transfusion reaction- ANTIBODY DETECTION

38
Q

What issues does Rh(D) cause in pregnancy?

A

Rh antibodies usually IgG - can cause haemolytic disease of newborn.

Anti-D most common cause of severe HDN`

39
Q

Outline how Haemolytic Disease of Newborn occurs

A
  1. Rh+ father
  2. Rh- mother carrying 1st Rh+ fetus.
    Antigens from developing fetus can enter mothers
    blood during pregnancy
  3. Mother produces anti-Rh antibodies in response to fetal
    Rh antigens
  4. If mother becomes pregnant with another Rh+ baby, her
    anti-Rh antibodies cross placenta and damage fetal rbcs
40
Q

How can we test for HDN?

A

Blood group and antibody screen at 28 wks; antenatal booking to identify pregnancies at risk of HDN

41
Q

Which patients are most at risk of HDN?

A

D negative women - may need anti-D prophylaxis

42
Q

How does the HDN screening test identify HDN risk patients?

A

Atypical antibodies are quantified periodically to assess their potential effect on the fetus

43
Q

What is RAADP?

A

Routine administration of anti-D immunoglobulin is called routine antenatal anti-D prophylaxis (RAADP)

44
Q

What is the purpose of RAADP?

A

An injection of anti-D will bind to and remove any fetal D positive red cells in the circulation - prevents HDN

45
Q

Describe the dosage of RAADP administered in utero and postnatally

A 
1500 iu anti-D given routinely at 28 weeks 
Smaller dose (usually 500 iu) after delivery if baby RhD+

In some hospitals 2 smaller (500 iu) doses are given at 28 and 34 weeks instead of 1 larger dose

46
Q

When else is Anti-D administered to pregnant women?

A

Anti-D also given after any event causing feto-maternal haemorrhage (bleed between mum and fetus) such as:

  • Abdominal trauma
  • Intrauterine death
  • Spontaneous or therapeutic abortion
47
Q

Why is antibody screening carried out?

A

Other clinically significant antibodies can cause a haemolytic transfusion reaction

If detected, antigen negative blood can be provided to avoid causing an immune reaction

48
Q

Outline the process of antibody screening

A
  1. Patient serum mixed with 3 selected screening cells
  2. Incubated for 15 minutes at 37c
  3. Centrifuge for 5 minutes
  4. Clinically significant antibodies reacting at body temp
    detected & identified using panel of known phenotyped
    red cells

Specific antigen -ve blood provided for patients to avoid stimulating immune response.

49
Q

What do we do if an antibody is detected in antibody screening?

A

Identify the antibody

Assess its clinical significance

  • For transfusion
  • In pregnancy
50
Q

How do we identify an antibody?

A

Compare pattern of reactions with each reagent cell of ID panel with the pattern of antigens on the reagent cells

Matching pattern will identify the antibody

51
Q

How does zeta potential immunoglobulins in circulation?

A

IgM antibodies can span gap between RBCs

IgG can’t, because too small to overcome ZETA potential (+ve charge)

52
Q

How do we overcoem zeta potential to allow IgG to span RBC gap?

A

LISS (low ionic strength saline) is negatively charged, so neutralises positive ZETA potential

IgG can now span the gap.

53
Q

When is an Indirect Antiglobulin test (IAT) carried out?

A

Used to detect IgG antibodies

LISS counteracts Zeta potential - results in agglutination

54
Q

What is an Indirect Antiglobulin Test ( IAT) used for?

A

Used for:
- Screening for antibodies
- Identifying antibodies
- Cross-matching donor blood with recipient plasma when
there are known antibodies / previous history of
antibodies

55
Q

What 2 methods are used for cross matching?

A
  • Immediate spin crossmatch (ISX)

- Full Indirect Antiglobulin test (IAT) cross-match

56
Q

Describe how an ISX cross match is carried out

A

Incubate for 2 – 5 minutes (room temp), centrifuge spin and read

57
Q

When is an ISX done?

A

Antibody screen is negative
Checking donor red cells against patients plasma

ABO check

58
Q

When is a full IAT cross match conducted?

A

Antibody screen positive or patient has known antibody history.

59
Q

Describe how a full IAT is carried out

A

Select antigen negative donor red cells and incubate with patient serum for 15 minutes at 37oC

60
Q

Why is an indirect antiglobulin test (IAT) not done in ISX?

A

ISX - checks ABO group.

Therefore IgM antibodies (therefore no problem with ZETA potential, therefore no need to IAT

61
Q

How many blood donors does NHS receive anually?

A

NHSBT collects about 2 million donations per year.

Only 4-6% of eligible population donate

62
Q

What makes an eligible donor?

A
  • 17 - 65 years old (first donation)

- Over 50kg

63
Q

What tests are carried out on a blood donor to ensure safe donation?

A

Blood Establishment
- MHRA licensed manufacturer of blood and products

Donor Selection
- Questionnaire: lifestyle, health, not previously transfused

Collection procedure arm cleansing / diversion pouch

Comprehensive testing of all products

  • Viral
  • HIV 1+2
  • Hepatitis B and C
  • Syphilis
  • HTLV

Platelets
- Bacteria

ABO, RhD, K, antibody screen

64
Q

What are the relative risks of transfusion?

A

1 in 1.2 million for Hepatitis B
1 in 28 million for Hepatitis C
1 in 7 million for HIV infection
1 in 23 million for HTLV infection

65
Q

When are red cells transfused?

A

Symptomatic anaemia

- If significant bleeding anticipated, activate the major haemorrhage protocol

66
Q

Describe the features of red cell transfusion

A

Concentrated red cells (packed cells) in a suspension of SAGM
Red cells oxygen carrying capacity
Exchange transfusion

67
Q

Why may fresh frozen plasma be transfused?

A

Given for coagulopathy with associated bleeding

68
Q

What does fresh frozen plasma contain that is useful for coaguopathic patients?

A

FFP contains all clotting factors

69
Q

What are the cosniderations of FFP transfusion?

A

Requires clotting screens to monitor

  • Only has 24 hour life after thawing
  • (five days for major haemorrhage)
70
Q

What is the significance of platelets?

A

Platelets required to create clots to reduce bleeding

71
Q

How are platelets transfused?

A

Adult pool of platelets from 4 donors (suspended in plasma from 1 donor)

72
Q

Why is it important to take medical history of plasma transfusion patients?

A

Some drugs given to reduce efficacy of platelets (antiplatelet agents) so patient history important

73
Q

What does a cryoprecipitate contain?

A

Contains Factor VIII, VWF and fibrinogen

74
Q

How much cryoprecipitate is transfused at a time?

A

2 units usually given at one time

Monitor fibrinogen levels by clotting screens

75
Q

How is blood donation regulated?

A
  • EU Blood Safety Directive
  • Blood Safety Quality Regulations
  • Better Blood Transfusion 3
  • MHRA inspections
  • CPA inspections
76
Q

What is haemovigilance?

A

Surveillance procedures covering entire blood transfusion chain:
Donation, processing of blood and its components, provision and transfusion to patients, and follow-up

77
Q

What are haemovigilance SHOTs?

A

Serious Hazards of Transfusion (SHOT):

  • Voluntary reporting
    Report all Serious adverse Events (SAE) and Serious adverse reactions (SAR)
78
Q

What are haemovigilance SABRE?

A

Serious Adverse Blood reactions and events (SABRE):

  • Mandatory reporting
    Report all SAR and SAE where the root cause error was the Quality system

Haematology (8 decks)

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