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SEM 4: Haematology > The Blood Transfusion Lab > Flashcards

The Blood Transfusion Lab Flashcards

1
Q

What are antigens?

A
  • Part of the surface of cells

- All blood cells have antigens

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2
Q

What are the antibodies?

A
  • Protein molecules such as immunoglobulins (Ig)
  • Usually of the immunoglobulin classes: IgG and IgM
  • Found in the plasma
  • Produced by the immune system following exposure to a foreign antigen.
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3
Q

What happens when antigens and antibodies interact?

A
  • Reactions to blood occur when the antibody in the plasma interacts with an antigen on the cells.
  • When the body is exposed to non-self antigens, it starts to produce antibodies by the immune system.
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4
Q

What are the Blood group antigens?

A
  • There are 26 known blood group systems

- ABO and Rh are clinically most important

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5
Q

How can antigens in transfused blood cause the production of antibodies?

A
  • Antigens in transfused blood can stimulate a patient to produce an antibody but only if the patient lacks the antigen themselves.
  • The frequency of antibody production is very low but increases the more transfusions that are given.
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6
Q

How are antibodies produced?

A
  • Blood transfusion: i.e. blood carrying antigens foreign to the patient
  • Pregnancy: i.e. 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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7
Q

Describe the antibody-antigen reactions in vivo

A

In the body:
- Leads to destruction of the cell either:
-> directly when the cell breaks up in the bloodstream (intravascularly)
-> indirectly when liver and spleen remove antibody coated cells (extravascularly)
It causes haemolysis indirect or direct.

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8
Q

Describe the antibody-antigen reactions in vitro

A

In the lab:

- Reactions are normally seen as agglutination tests

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9
Q

What is agglutination?

A
  • The clumping together of red cells into visible agglutinates by antigen-antibody reactions. Not coagulation
  • Result of antibody cross-linking with the antigens
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10
Q

Why is agglutination important?

A
  • It is specific so it can be used to identify the red cell antigens present.
  • It can also identify the presence of an antibody in the plasma.
  • Red cells of a known specificity can be used to detect antibodies in a patients plasma
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11
Q

What is the clinical significance of the ABO grouping system?

A
  • Almost all serious/fatal transfusion reactions are caused by technical/clerical error due to ABO incompatibility
  • ABO antibodies can activate complement causing intravascular haemolysis
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12
Q

How do ABO groups work?

A
  • A person who has blood type A - will have antigen A present in their blood and Anti-B antibodies. They will only be able to receive blood from type A or type O not type AB or type B.
  • A person who has blood type B -will have antigen B present in their blood and Anti-A antibodies. they will only be able to receive blood from type B or type O not type AB or type A.
  • A person who has blood type O will have no antigens present on their blood and will have anti-A and anti-B. They are able to give blood to all blood types but only receive blood from type O patients.
  • A person who has type AB will have both the A and B antigens present but no antibodies. They are able to receive blood from all blood groups and give blood to only type AB.
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13
Q

What is present in gut bacteria?

A

Gut bacteria have A-like and B-like antigens; exposure to these gut bacteria will recognize the specific antigens as self, but the other antigens will be recognized as non-self. This will stimulate the immune system and produce antibodies.

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14
Q

Describe blood grouping using red cells

A
  1. Test the patient’s blood with anti-A, anti-B, and anti-D.
  2. Agglutination will occur.
  3. If the blood agglutinations with anti-A, it means that antigen A is present. Likewise, if there is agglutination with anti-B, it means antigen B is present.
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15
Q

Describe blood grouping using plasma

A
  1. Test the patient’s blood with A cells and B cells.
  2. Agglutination can occur.
  3. If testing with A cells, and it agglutinates, this means there are anti-B present so the person is type B. This is the same when testing with B cells.
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16
Q

Describe blood grouping with anti-D

A
  1. Add patient’s blood and spin
  2. Agglutination occurs and cannot pass through the gel matrix if it is too big.
  3. If no agglutination occurs, the RBC go straight through.
    This shows that anti-D is present if it agglutinates.
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17
Q

Describe ABO compatibility

A
  • O- can be given to anyone as it doesn’t react with antigens in the blood.
  • Type A pts can receive blood from type A and O-.
  • Type B pts can receive blood from type B and O-.
  • Type O pts can receive only O blood but can give blood to anyone.
  • Type AB pts can receive blood from O, A, B, and AB but only give blood to type AB.
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18
Q

What is the Rh grouping system?

A
  • Comprised of 50+ antigens.
  • The 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.
19
Q

How is Rh (D) typing done?

A
  • Most important after ABO
  • Must be tested in duplicate (or tested each time and compared to historical result)
  • Patient/Donor classified as D pos or D neg
20
Q

What is the clinical significance of Rh?

A
  1. During transfusion:
    - The D antigen is very immunogenic and anti-D is easily stimulated so this needs to be prevented in case of rejection.
    - All Rh antibodies are capable of causing severe transfusion reaction through antibody detection.
  2. Pregnancy:
    - Rh antibodies are usually IgG and can cause haemolytic disease of the newborn.
    - Anti-D is still the most common cause of severe HGN.
21
Q

What is haemolytic disease of the newborn (HDN)?

A
  1. The mother can be Rh- mother and carry her first child which could be Rh+. The Rh antigens from the developing fetus can enter the mother’s blood during delivery.
  2. In response to the fetal Rh antigens, the mother will produce anti-Rh antibodies.
  3. If the woman becomes pregnant with another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells.
22
Q

How is HDN tested for?

A
  • Blood group and antibody screening at antenatal booking to identify pregnancies at risk of HDN: D- negative women may need anti-D prophylaxis.
  • Blood group and antibody screen at 28 weeks
  • Atypical antibodies are quantified periodically to assess their potential effect on the fetus
23
Q

What is RAADP?

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, and spontaneous or therapeutic abortion
24
Q

Why is antibody (anti-D) screening important?

A
  • There are other clinically significant antibodies that can cause a haemolytic transfusion reaction.
  • Important to screen for antibodies so that if detected, antigen-negative blood can be provided to avoid causing an immune reaction
25
Q

Describe the process of antibody (anti-D) screening

A
  1. The patient’s serum is mixed with 3 selected screening cells, incubated for 15 minutes at 37oC, and then centrifugated for 5 minutes.
  2. Any clinically significant antibodies reacting at body temperature should be detected, and then identified using a panel of known phenotyped red cells.
  3. Specific antigen-negative blood can then be provided for these patients to avoid stimulating an immune response.
26
Q

What happens when an antibody (anti-D) is detected?

A
  • Identify the antibody

- Assess its clinical significance: for transfusion and in pregnancy

27
Q

How to identify an antibody that is present?

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
28
Q

What is an ID panel?

A

Used to identify all the antibodies present in the blood

ID-cells with antigens using the indirect antiglobulin test (IAT)

29
Q

What is the zeta potential between red blood cells, IgG, and IgM?

A
  • IgM antibodies can span the gaps between RBCs whereas IgGs cannot because they’re too small to overcome zeta potential (+ve charge).
  • IgG is pentameric and big. The RBC cannot get close as there is a positively charged cloud. IgM can get close and cause agglutination but IgG cannot.
  • The ABO antibodies are IgM; almost all the others are IgG (anti-D).
  • LISS (low ionic strength saline) is negatively charged, so neutralises positive zeta potential. Therefore, IgG can now span the gap.
30
Q

What is the indirect anti-globulin test (IAT)? Why is it used?

A
  • Used to detect IgG antibodies
  • LISS counteracts Zeta Potential
  • Results in agglutination
  • Used for:
    • > Screening for antibodies
    • > Identifiying antibodies
    • > Cross-matching donor blood with recipient plasma when there are known antibodies or a previous history of antibodies
31
Q

What is cross-matching donor blood?

A

Used with recipient plasma when there are known antibodies or a previous history of antibodies

32
Q

What are the cross-matching tests done?

A
  • Immediate spin cross-match (ISX): antibody screen is negative then checking donor red cells against the patient’s plasma (ABO check and incubate for 2- 5 minutes (room temp), spin and read).
  • Full Indirect Antiglobulin Test (IAT) cross-match: antibody screen positive or the patient has known antibody history. Then, select antigen-negative donor red cells and incubate with patient serum for 15 minutes at 37oC.
33
Q

What happens if ISX shows no problem with zeta potential?

A

ISX basically checking the ABO group. Therefore, IgM antibodies, therefore no problem with zeta potential, therefore no need to IAT.

34
Q

What is a negative and positive ISX?

A

If the blood agglutinates, it is positive. If it doesn’t, it is negative. This is opposite to the gel cards where agglutinated products stay at the top. There is agglutination, there is a pellet at the bottom.

35
Q

Why are blood donors important?

A
  • NHSBT collects about 2 million donations per year.
  • Only 4-6% of the eligible population donate
  • Eligibility: 17-65 years old (first donation) and/or over 50 years
36
Q

How is donor blood testing carried out?

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 and HTLV
  • Platelets: Bacteria
  • ABO, RhD, K, Antibody screen
37
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
  • There are believed to have been 4 cases of infected with vCJD from a blood transfusion
38
Q

When are red cell transfusions given?

A
  • Concentrated red cells (packed cells) in a suspension of SAGM
  • Red cells oxygen-carrying capacity
  • Symptomatic anaemia
  • Exchange transfusion
  • If significant bleeding anticipated, activate the major haemorrhage protocol.
39
Q

When are fresh frozen plasma transfusions given?

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)
40
Q

When are platelets transfusions given?

A
  • The adult pool of platelets from 4 donors (suspended in plasma from 1 donor)
  • Platelets required to create clots to reduce bleeding
  • Some drugs are given to reduce the efficacy of platelets (anti-platelet agents) so patient history is important
41
Q

When are cryoprecipitate transfusions given?

A
  • Contains factor VIII, VWF and fibrinogen
  • 2 units are usually given at one time
  • Monitor fibrinogen levels by clotting screen
42
Q

How are blood transfusions regulated?

A
  • EU blood safety directive
  • Blood Safety Quality Regulations
  • Better Blood Transfusion 3
  • MHRA inspections
  • CPA inspections
43
Q

What is haemovigilance?

A
  • Serious Hazards of Transfusion (SHOT): Voluntary reporting and Report all Serious adverse Events (SAE) and Serious adverse reactions (SAR)
  • Serious Adverse Blood reactions and events (SABRE): Mandatory reporting and Report all SAR and SAE were the root cause error was the Quality system

SEM 4: Haematology (8 decks)

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