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
2
Q
When do reactions in blood usually occur?
A
- When the antibody in the plasma reacts with an antigen on the cells
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
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
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
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
7
Q
What is agglutination?
A
- The clumping together of red cells into visible agglutinates by antigen-antibody reactions
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
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)
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
11
Q
Describe the genetics of the ABO blood group system
A
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
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
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
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
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
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)
18
Q
Explain the clinical significance of the Rh blood grouping system
A
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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
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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
Describe how antibody screening is carried out
* 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
What happens if i clinically significant antibody is detected durinf an antibody screen?
* Identify the antibody
* Assess its clinical significance
* For transfusion
* In pregnancy
27
How do you identify an antibody?
* 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
What is the Zeta potential?
* Positively charged ionic cloud that surronds a red blood cell
29
What effect does zeta potential have on agglutination?
* 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
Why are IgG antibodies unable to cause agglutination?
* IgG can not, because they are too small to overcome ZETA potential
31
What is LISS?
* LISS (low ionic strength saline) is negatively charged and so neutralises positive ZETA potential
* This allows IgG antibodies to cause agglutination
32
How are IgG antibodies detected?
* Indirect anti-globulin test (IAT)
* Uses LISS to counteract Zeta potential which allows for IgG to cause agglutination
33
What is the Indirect anti-globulin test (IAT) 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.
34
What are the 2 different types of cross-matching?
* **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
What criteria does a person have to meet in order to be eligible to donate blood?
* 17 - 65 years old (first donation)
* Over 50kg
36
State some relative risks of transfusion
* 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
What are the 4 main components of blood?
* Red cells
* Plasma
* Platelets
* Cryoprecipitate
38
Describe how red cells are transfused and state when a red cell transfusion is given
* 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
Describe how plasma is transfused and state when a plasma transfusion is given
* 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
Describe how platelets are transfused and state when a platelet transfusion is given
* 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
Describe how the cyroprecipitate is transfused and state when a cryoprecipitate transfusion is given
* 2 units usually given at one time
* Monitor fibrinogen levels by clotting screens during transfusion
42
What bodies regulate blood donation?
* EU Blood Safety Directive
* Blood Safety Quality Regulations
* Better Blood Transfusion 3
* MHRA inspections
* CPA inspections
43
What systems are put into place for hemovigilance reporting?
* **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
