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Clinical pathology specialities: Haematology > Haematology: The Blood Transfusion Lab > Flashcards

Haematology: The Blood Transfusion Lab Flashcards

1
Q

What is the difference between antibodies and antigens?

A
  • Antigens are part of the surface of cells
    • All blood cells have antigens
  • Antibodies are protein molecules –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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2
Q

When do reactions in blood usually occur?

A
  • When the antibody in the plasma reacts with an antigen on the cells
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3
Q

How many known blood group systems are there and which are the most important clinically?

A
  • 26 known blood group systems
  • ABO and Rh are clinically most important
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4
Q

What happens to antibody production as a result of a blood transfusion?

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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5
Q

What things are able to stimulate antibody production?

A
  • Blood transfusion - blood carrying antigens foreign to the patient
  • Pregnancy - Fetal antigens enter maternal circulation during pregnancy or at birth
  • Environmental factors - Natural acquisition of antigens, e.g. Anti-A and anti-B
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6
Q

What are the different types of Antibody-Antigen reactions?

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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7
Q

What is agglutination?

A
  • The clumping together of red cells into visible agglutinates by antigen-antibody reactions
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8
Q

What things can agglutination be used to identify?

A
  • The presence of a red cell antigen - e.g. particular blood group
  • The presence of an antibody in the plasma - e.g. antibody screening/identification
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9
Q

How common are A and B antigens within the population and how common are the antibodies for these antigens?

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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10
Q

What does the fact that A and B antigens, as well as their antibdies, are quite common within the population mean for blood transfusion?

A
  • It means there’s a high risk of A or B antigens being transfused into someone with the antibody for either A or B antigens in a random situation
  • This is quite dangerous because ABO antibodies can activate complement causing intravascular haemolysis
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11
Q

Describe the genetics of the ABO blood group system

A
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12
Q

State the antibodies and antigens present in each of the different ABO blood groups

A
  • Blood group A
    • Antibodies present: Anti-B
    • Antigens present: A antigen
  • Blood group B
    • Antibodies present: Anti A
    • Antigens present: B antigen
  • Blood group AB
    • Antibodies present: None
    • Antigens present: A and B antigens
  • Blood group O
    • Antibodies present: Anti-A and Anti-B
    • Antigens present: No antigens
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13
Q

Explain how a person who’s blood group A has Anti-B antibodies, specific to B antigens, within their blood since they don’t have any B antigens within their plasma

A
  • Antibodies are produced in response to exposure to non-self antigens
  • This means that in order for a person who’s blood group A to have Anti-B antibodies they must have been exposed to B antigens
  • This exposure occurs because there are gut bacteria that have A-like and B-like antigens on their surface
  • When baby is in the uterus it’s exposed to these bacteria and because the B-like antigens are recognised as foreign it results in the production of Anti-B antigens
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14
Q

How would you identify a patients ABO blood group using lab testing?

A
  • Gel card with 6 wells
  • First 4 wells contain : Anti-A, Anti-B, Anti-D and a control
  • Add some of patients red cells to each of the 4 wells, incubate and then spin the gel card
  • You then see if agglutination has occured
    • Agglutination shows that a particular antigen is on the red cells
    • No agglutination shows the antigen is absent
  • The final 2 wells contain Blood group A red cells (A1) and blood group B red cells
  • Add patient’s plasma to these wells, incubate and spin gel card and then see if agglutination occurs
    • Agglutination shows that a particular antibody is in the plasma or serum
    • No agglutination shows the antibody is absent
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15
Q

Describe the compatibility of each of the ABO blood groups with each other

A
  • Blood group O: Comaptible with all ABO blood groups
  • Blood group A: Compatible with blood groups A and AB
  • Blood group B: Compatible with blood groups B and AB
  • Blood group AB: Only compatible with AB blood group
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16
Q

Describe main features of Rh blood grouping system

A
  • 50+ antigens
  • Most important antigen is called D
  • People with D antigen are D positive (85% of UK)
  • People who don’t produce any D antigen are D negative (15%)
  • The other 4 main antigens are known as C, c, E and e
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17
Q

Describe the process of Rh (D) typing

A
  • Same process of ABO blood group testing - place Anti-D into a gel card well; add patients blood; incubate and spin gel card and see if agglutination occurs
  • Must be tested in duplicate (or tested each time and compared to historical result)
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18
Q

Explain the clinical significance of the Rh blood grouping system

A
  • Transfusion
    • D antigen is very immunogenic and anti-D is easily stimulated so if Rh (D)- person is transfused with Rh (D)+ blood transfustion reaction vERY likely to occur
    • All Rh antibodies are capable of causing severe transfusion reaction
  • Pregnancy
    • Rh antibodies are usually IgG and can cause haemolytic disease of the newborn (HDN).
    • Anti-D is still most common cause of severe HDN
19
Q

Explain how haemolytic disease of the newborn can develop during pregnancy

A
  • You have an Rh+ father and a pregnant Rh- mother
  • Mother is carrying an Rh+ foetus
  • RBCs with Rh antigens can enter matrnal circulation during delivery
  • Because mother is Rh- the Rh antigens are recognised as “foreign” so mother produces anti-Rh antibodies
  • If woman becomes pregnant with another Rh+ foetus, Anti-Rh antibodies from mother will cross placenta and damage foetal red cells
20
Q

How can laboratory screening be used to prevent Haemolytic disease of the newborn (HDN)?

A
  • Blood group and antibody screen at antenatal booking to identify pregnancies at risk of HDN
    • Rh (D) negative women who may need anti-D prophylaxis
  • Blood group and antibody screen at 28 weeks
  • Any unusual antibodies identified during either screening are quantified to assess their potential effect on the foetus
21
Q

What is RAADP?

A
  • RAADP (Routine antenatal anti-D prophylaxis) is a prevention treatment given to Rh(D) negative pregnant women to prevent HDN
  • It involves the woman being given an injection of anti-D which will bind to and remove any fetal D positive red cells in the circulation
22
Q

What does of anti-D is given during RAADP?

A
  • 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
23
Q

During what other events/conditions may anti-D be administered?

A
  • May also be given after an event that may cause a feto-maternal haemorrhage such as:
    • Abdominal trauma
    • Intrauterine death
    • Spontaneous or therapeutic abortion
24
Q

Why is antibody screening important?

A
  • Because there are lots of clinically significant antibodies that can cause a haemolytic transfusion reaction.
  • It’s important that we screen for these antibodies so that, if detected, antigen negative blood can be provided to avoid causing an immune reaction
25
Q

Describe how antibody screening is carried out

A
  • Patients serum is mixed with 3 selected screening cells, incubated for 15 minutes at 37°C 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.
26
Q

What happens if i clinically significant antibody is detected durinf an antibody screen?

A
  • Identify the antibody
  • Assess its clinical significance
    • For transfusion
    • In pregnancy
27
Q

How do you identify an antibody?

A
  • Compare the pattern of reactions with each reagent cell within the ID panel with the pattern of antigens on the reagent cells
  • Matching pattern will identify the antibody
28
Q

What is the Zeta potential?

A
  • Positively charged ionic cloud that surronds a red blood cell
29
Q

What effect does zeta potential have on agglutination?

A
  • Zeta potential of RBCs means that they can’t get close to each other as positively charged ionic clouds will repel against each other
  • Repulsion means there’s a gap between each RBC
  • This means that only way for agglutination to occur is an IgM antibody coming in and spanning the gap between 2 RBCs.
30
Q

Why are IgG antibodies unable to cause agglutination?

A
  • IgG can not, because they are too small to overcome ZETA potential
31
Q

What is LISS?

A
  • LISS (low ionic strength saline) is negatively charged and so neutralises positive ZETA potential
  • This allows IgG antibodies to cause agglutination
32
Q

How are IgG antibodies detected?

A
  • Indirect anti-globulin test (IAT)
  • Uses LISS to counteract Zeta potential which allows for IgG to cause agglutination
33
Q

What is the Indirect anti-globulin test (IAT) used for?

A
  • Screening for antibodies
  • Identifying antibodies
  • Cross-matching donor blood with recipient plasma when there are known antibodies or a previous history of antibodies.
34
Q

What are the 2 different types of cross-matching?

A
  • Immediate spin cross-match (ISX)
    • ​​Done if antibody screen is negative
    • Checks donor red cells against patients plasma
    • Essentially an ABO check
    • Incubate for 2 – 5 minutes (room temp), spin and read.
  • Full Indirect Antiglobulin test (IAT) cross-match
    • ​Only done if antibody screen positive or patient has known antibody history.
    • Select antigen negative donor red cells and incubate with patient serum for 15 minutes at 37°C
35
Q

What criteria does a person have to meet in order to be eligible to donate blood?

A
  • 17 - 65 years old (first donation)
  • Over 50kg
36
Q

State some 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
37
Q

What are the 4 main components of blood?

A
  • Red cells
  • Plasma
  • Platelets
  • Cryoprecipitate
38
Q

Describe how red cells are transfused and state when a red cell transfusion is given

A
  • Transfused red cells given as concentrated red cells (packed cells) in a suspension of SAGM
  • Transfusion carried out as exchange transfusion
  • Given for Symptomatic anaemia
  • NOTE: If significant bleeding anticipated, activate the major haemorrhage protocol
39
Q

Describe how plasma is transfused and state when a plasma transfusion is given

A
  • Fresh frozen plasma is thawed out and then transfused into patient
  • Only has 24 hour life after thawing (five days for major haemorrhage)
  • Requires clotting screens to monitor during transfusion
  • Given for Coagulopathy with associated bleeding
40
Q

Describe how platelets are transfused and state when a platelet transfusion is given

A
  • Platelets to be transfused made up of adult pool of platelets from 4 donors (suspended in plasma from 1 donor)
  • Some drugs given to reduce efficacy of platelets (anti-platelet agents) so patient history important
  • Given to create clots to reduce bleeding
41
Q

Describe how the cyroprecipitate is transfused and state when a cryoprecipitate transfusion is given

A
  • 2 units usually given at one time
  • Monitor fibrinogen levels by clotting screens during transfusion
42
Q

What bodies regulate blood donation?

A
  • EU Blood Safety Directive
  • Blood Safety Quality Regulations
  • Better Blood Transfusion 3
  • MHRA inspections
  • CPA inspections
43
Q

What systems are put into place for hemovigilance reporting?

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

Clinical pathology specialities: Haematology (8 decks)

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