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2 - Clinical Biochemistry > blood transfusion lab > Flashcards

blood transfusion lab Flashcards

1
Q

what are antigens?

A

part of the surface of cells

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2
Q

all blood cells have what?

A

antigens

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3
Q

what are antibodies?

A

protein molecules –usually of the immunoglobulin classes: IgG and IgM

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4
Q

when do reactions to blood usually occur?

A

when the antibody in the plasma reacts with an antigen on the cells

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5
Q

where are antibodies found?

A

in the plasma

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6
Q

when are antibodies produced?

A

produced by the immune system following exposure to a foreign antigen

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7
Q

how many known blood group systems are there?

A

26

-ABO and Rh are clinically most important

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8
Q

antigens in transfused blood can stimulate what?

A

can stimulate a patient to produce an antibody, but ONLY if the patient lacks the antigen themselves

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9
Q

is the frequency of antibody production high or low?

A

very low but increases the more transfusions that are given

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10
Q

when is antibody production stimulated?

A

Blood transfusion
-i.e. blood carrying antigens foreign to the patient

Pregnancy
-fetal antigen entering maternal circulation during pregnancy or at birth

Environmental factors
-(i.e. naturally acquired e.g. anti-A and anti-B)

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11
Q

where do Antibody – Antigen reactions occur?

A

in vivo (in the body)

  • leads to the destruction of the cell either:
    - directly when the cell breaks up in the blood stream (intravascular)
    - indirectly when liver and spleen remove antibody coated cells (extravascular)
in vitro (in the laboratory)
-reactions are normally seen as agglutination tests
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12
Q

define agglutination

A

clumping together of red cells into visible agglutinates due to antigen-antibody reactions (antibody cross-linking with the antigens)

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13
Q

what is specific?

A

the antigen-antibody reaction agglutination can identify:-

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14
Q

what can agglutination identify?

A

The presence of a red cell antigen
-i.e. blood grouping

The presence of an antibody in the plasma
-i.e. antibody screening/identification

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15
Q

55% of the UK have which antigens?

A

A and B antigens

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16
Q

97% UK have which anti bodies?

A

Anti-A, anti-B or anti-A,B antibodies

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17
Q

what is high risk?

A

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

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18
Q

ABO antibodies can activate what?

A

complement

-causing INTRAVASCULAR HAEMOLYSIS

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19
Q

almost all serious/fatal transfusion reactions caused by technical/clerical error are due to what?

A

ABO incompatibility

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20
Q

blood type phenotypes, antigens and antibodies

A

groups A, B, AB, O
antigens A, B, A + B, no antigens
antibodies anti-B, anti-A, anti-A and anti-B, none

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21
Q

what happens in a blood grouping test?

A

patient’s red cells and plasma are both tested

  1. Test patient’s red cells with anti-A, anti-B and anti-D
    - agglutination shows that a particular antigen is on the red cells
    - no agglutination shows the antigen is absent
  2. Test patient’s plasma with A cells and B cells
    - agglutination shows that a particular antibody is in the plasma or serum
    - no agglutination shows the antibody is absent
22
Q

ABO Compatibility

  1. who can O blood types donate to?
  2. who can A blood types donate to?
  3. who can B blood types donate to?
  4. who can AB blood types donate to?
A
  1. O, A, B, AB
  2. A, AB
  3. B, AB
  4. AB
23
Q

other than the ABO grouping system, what is other blood grouping system in the body?

A

Rh grouping system

  • RBC’s sometimes have another antigen, a protein known as the RhD antigen
  • If this is present, your blood group is RhD positive
  • If it’s absent, your blood group is RhD negative
24
Q

what is the most important antigen in the Rh grouping system?

A

D

25
Q

people with the D antigen are what?

A

D positive (85% of UK)

26
Q

people who don’t produce any D antigen are what?

A

D negative (15%)

27
Q

name the antigens involved in the Rh grouping system

A

antigens: D, C, c, E and e

28
Q

what typing is most important after ABO and how does it work?

A

Rh (D) typing

  • must be tested in duplicate or tested each time and compared to historical result
  • patient / donor classified as D pos or D neg
29
Q

Clinical significance of Rh

-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
30
Q

Clinical significance of Rh

-Pregnancy

A
  • Rh antibodies are usually IgG and can cause haemolytic disease of the newborn
  • Anti-D is still most common cause of severe HDN
31
Q

what occurs in Haemolytic disease of the Newborn (HDN)

A

Rh- mother carries a Rh+ foetus. Rh antigens can from the foetus can enter the mothers blood during delivery. In response to the foetal Rh antigens, the mother produces Anti-Rh antibodies. If the mother becomes pregnant with another Rh+ foetus, the anti-Rh antibodies could cross the placenta and damage foetal RBC’s.

32
Q

HDN – laboratory testing

A

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

D negative women who may need anti-D prophylaxis

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

33
Q

the scan at 28 weeks looks at what?

A

Blood group and antibody screen

34
Q

how can HDN be prevented?

A

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

1500 iu of anti-D is given routinely at 28 weeks and a 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 the 1 larger dose

Anti-D is also given after any event that may cause a feto-maternal haemorrhage (bleed between mum and fetus) such as:
Abdominal trauma
Intrauterine death
Spontaneous or therapeutic abortion

35
Q

why is Antibody Screening important?

A

its important we screen for these antibodies so that if detected, antigen negative blood can be provided to avoid causing a immune reaction
-prevent a haemolytic transfusion reaction

36
Q

how does Antibody screening work?

A

Patients serum is mixed with 3 selected screening cells, incubated for 15 minutes at 37oc and then centrifuged for 5 minutes.

Any clinically significant antibodies reacting at body temp should be detected and then identified using panel of known phenotyped red cells.

Specific antigen negative blood can then be provided for these patients to avoid stimulating an immune response.

37
Q

If an antibody is detected we must?

A

Identify the antibody

Assess its clinical significance

  • For transfusion
  • In pregnancy
38
Q

How to 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

39
Q

IgG vs IgM?

A

IgM antibodies can span the gap between RBCs

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

40
Q

how can IgG span the gap - what modification happens?

A

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

Therefore IgG can now span the gap.

41
Q

Indirect anti-globulin test (IAT)

A

Used to detect IgG antibodies

LISS counteracts Zeta potential

Results in agglutination

Used for:

  • Screening for antibodies
  • Identifying antibodies
  • Cross-matching donor blood with recipient plasma when there are known antibodies or a previous history of antibodies.
42
Q

Cross-matching?

A

Immediate spin cross-match (ISX)

Full Indirect Antiglobulin test (IAT) cross-match
-only if Antibody screen positive or patient has known antibody history

43
Q

Immediate spin cross-match (ISX)

A

basically checking the ABO blood group, and with IgM antibodies there is no ZETA potential, therefore no need to IAT

Antibody screen is negative

Checking donor red cells against patients plasma

    - ABO check
     - Incubate for 2 – 5 minutes (room  temp), spin and read
44
Q

Full Indirect Antiglobulin test (IAT) cross-match

A

Antibody screen positive or patient has known antibody history

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

45
Q

Blood donors

A

Only 4-6% of eligible population donate

Eligibility:
17 - 65 years old (first donation)
Over 50kg

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
Hepatitis C
Syphilis
HTLV

Platelets

Bacteria

ABO, RhD, K, antibody screen

46
Q

Relative risks of transfusion for HIV?

A

1 in 7 million for HIV infection

47
Q

how does transfusion of red cells work?

A

Concentrated red cells (packed cells) in a suspension of SAGM
-with symptomatic anaemia you can do an exchange transfusion

If significant bleeding anticipated, activate the major haemorrhage protocol

48
Q

transfusion of Fresh Frozen Plasma?

A

FFP contains all clotting factors

Given for coagulopathy with associated bleeding

Requires clotting screens to monitor

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

49
Q

transfusion of Platelets?

A

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

Platelets required to create clots to reduce bleeding

Some drugs given to reduce efficacy of platelets (anti-platelet agents) so patient history important

50
Q

Cryoprecipitate

A

Contains Factor VIII, VWF and fibrinogen

2 units usually given at one time

Monitor fibrinogen levels by clotting screens

51
Q

Haemovigilance

A

Serious Hazards of Transfusion (SHOT):

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

Serious Adverse Blood reactions and events (SABRE):
-Mandatory reporting

2 - Clinical Biochemistry (10 decks)

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