The Blood Transfusion Lab Flashcards
What are antigens?
Antigens are part of the surface of cells
All blood cells have antigens
What are antibodies?
Antibodies are protein molecules –immunoglobulins (Ig)
Usually of immunoglobulin classes: IgG and IgM
Where are antibodies found?
Found in the plasma
How are antibodies produced?
Produced by the immune system following exposure to a foreign antigen
What causes reactions to blood transfusion?
Reactions to blood usually occurs when the antibody in the plasma reacts with an antigen on the cells
How many blood groups are there?
There are 26 known blood group systems - ABO and Rh are clinically most important
Why do patients ‘reject’ transufused blood?
Antigens in transfused blood can stimulate a patient to produce an antibody but only if the patient lacks the antigen themselves
How often are antibodies produced in a transfused patient?
The frequency of antibody production is very low but increases the more transfusions that are given
What procedures stimulate antibody production?
- Blood transfusion
- Pregnancy
Environmental factors
How does blood transfusion stimulate antibody production?
blood carrying antigens foreign to the patient
How can pregnancy stimulate antibody formation?
Fetal antigen entering maternal circulation during pregnancy or at birth
Describe how environmental factors contribute to antibody production
i.e. naturally acquired e.g. anti-A and anti-B
Outline an antigen-antibody reaction in vivo
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
Describe an antigen-antibody reaction in vitro
In vitro (in the laboratory) reactions are normally agglutination tests
What is agglutination?
Agglutination is the clumping together of red cells into visible agglutinates by antigen-antibody reactions
What causes agglutination?
Agglutination results from antibody cross-linking with the antigens
What is the significance of agglutination tests?
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
What are common blood groups?
A and B antigens very common (55% UK)
Anti-A, anti-B or anti-A,B antibodies very common (97% UK)
What is a common error of transfusion in emergencies
High risk of A or B cells being transfused into someone with the antibody in a random situation
WHat is the effect of ABO transfusion?
ABO antibodies can activate complement causing INTRAVASCULAR HAEMOLYSIS
What is a common consequence of ABO transfusion error
(Almost) all serious / fatal transfusion reactions caused by technical / clerical error are due to ABO incompatibility
Outline the genetics of a patient with blood type A
Phenotype: A
RBC Antigen: A
Genotype: AA or AO
RBC Antibody: B
Describe the genetics of patients with Blood type B
Phenotype: B
RBC Antigen: B
Genotype: BB or BO
RBC Antibody: A
Outline genetics of Blood type O patients
Phenotype: O
RBC Antigen: none
Genotype: OO
RBC Antibody: A and B
Describe the genetics of patients with blood type AB
Phenotype: AB
RBC Antigen: A and B
Genotype: AB
RBC Antibody: none
How do we determine a blood type?
The patient’s red cells and plasma are both tested
Describe a blood grouping test done on blood
Test patient’s red cells with anti-A, anti-B and anti-D
- agglutination = particular antigen on red cells
- no agglutination = antigen is absent
Outline how plasma is tested for blood type
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
Outline blood compatibility for O blood group people
Can only receive blood from Group O
What blood donor groups are compatible for A type blood?
Can receive blood from other A types or O type blood
Who can Blood type B patients receive blood from?
Can receive blood from other B types or O type blood
Which blood groups are compatible fro AB patients?
AB patients can receive blood from O, A, B and AB blood type donors
Describe the Rh grouping system
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
How is Rh(d) testing carried out?
Must be tested in duplicate (or tested each time and compared to historical result)
How are Rh(D) test result classified?
Patient / Donor classified as D pos or D neg
How significant are Rh antibodies?
Rh antibodies are clinically significant, Second only to ABO
How does Rh(D) react in transfusion?
D antigen is very immunogenic and anti-D is easily stimulated - PREVENTION!
All Rh antibodies are capable of causing severe transfusion reaction- ANTIBODY DETECTION
What issues does Rh(D) cause in pregnancy?
Rh antibodies usually IgG - can cause haemolytic disease of newborn.
Anti-D most common cause of severe HDN`
Outline how Haemolytic Disease of Newborn occurs
- Rh+ father
- Rh- mother carrying 1st Rh+ fetus.
Antigens from developing fetus can enter mothers
blood during pregnancy - Mother produces anti-Rh antibodies in response to fetal
Rh antigens - If mother becomes pregnant with another Rh+ baby, her
anti-Rh antibodies cross placenta and damage fetal rbcs
How can we test for HDN?
Blood group and antibody screen at 28 wks; antenatal booking to identify pregnancies at risk of HDN
Which patients are most at risk of HDN?
D negative women - may need anti-D prophylaxis
How does the HDN screening test identify HDN risk patients?
Atypical antibodies are quantified periodically to assess their potential effect on the fetus
What is RAADP?
Routine administration of anti-D immunoglobulin is called routine antenatal anti-D prophylaxis (RAADP)
What is the purpose of RAADP?
An injection of anti-D will bind to and remove any fetal D positive red cells in the circulation - prevents HDN
Describe the dosage of RAADP administered in utero and postnatally
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
When else is Anti-D administered to pregnant women?
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
Why is antibody screening carried out?
Other clinically significant antibodies can cause a haemolytic transfusion reaction
If detected, antigen negative blood can be provided to avoid causing an immune reaction
Outline the process of antibody screening
- Patient serum mixed with 3 selected screening cells
- Incubated for 15 minutes at 37c
- Centrifuge for 5 minutes
- 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.
What do we do if an antibody is detected in antibody screening?
Identify the antibody
Assess its clinical significance
- For transfusion
- In pregnancy
How do we identify an antibody?
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
How does zeta potential immunoglobulins in circulation?
IgM antibodies can span gap between RBCs
IgG can’t, because too small to overcome ZETA potential (+ve charge)
How do we overcoem zeta potential to allow IgG to span RBC gap?
LISS (low ionic strength saline) is negatively charged, so neutralises positive ZETA potential
IgG can now span the gap.
When is an Indirect Antiglobulin test (IAT) carried out?
Used to detect IgG antibodies
LISS counteracts Zeta potential - results in agglutination
What is an Indirect Antiglobulin Test ( IAT) used for?
Used for:
- Screening for antibodies
- Identifying antibodies
- Cross-matching donor blood with recipient plasma when
there are known antibodies / previous history of
antibodies
What 2 methods are used for cross matching?
- Immediate spin crossmatch (ISX)
- Full Indirect Antiglobulin test (IAT) cross-match
Describe how an ISX cross match is carried out
Incubate for 2 – 5 minutes (room temp), centrifuge spin and read
When is an ISX done?
Antibody screen is negative
Checking donor red cells against patients plasma
ABO check
When is a full IAT cross match conducted?
Antibody screen positive or patient has known antibody history.
Describe how a full IAT is carried out
Select antigen negative donor red cells and incubate with patient serum for 15 minutes at 37oC
Why is an indirect antiglobulin test (IAT) not done in ISX?
ISX - checks ABO group.
Therefore IgM antibodies (therefore no problem with ZETA potential, therefore no need to IAT
How many blood donors does NHS receive anually?
NHSBT collects about 2 million donations per year.
Only 4-6% of eligible population donate
What makes an eligible donor?
- 17 - 65 years old (first donation)
- Over 50kg
What tests are carried out on a blood donor to ensure safe donation?
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
What are the 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
When are red cells transfused?
Symptomatic anaemia
- If significant bleeding anticipated, activate the major haemorrhage protocol
Describe the features of red cell transfusion
Concentrated red cells (packed cells) in a suspension of SAGM
Red cells oxygen carrying capacity
Exchange transfusion
Why may fresh frozen plasma be transfused?
Given for coagulopathy with associated bleeding
What does fresh frozen plasma contain that is useful for coaguopathic patients?
FFP contains all clotting factors
What are the cosniderations of FFP transfusion?
Requires clotting screens to monitor
- Only has 24 hour life after thawing
- (five days for major haemorrhage)
What is the significance of platelets?
Platelets required to create clots to reduce bleeding
How are platelets transfused?
Adult pool of platelets from 4 donors (suspended in plasma from 1 donor)
Why is it important to take medical history of plasma transfusion patients?
Some drugs given to reduce efficacy of platelets (antiplatelet agents) so patient history important
What does a cryoprecipitate contain?
Contains Factor VIII, VWF and fibrinogen
How much cryoprecipitate is transfused at a time?
2 units usually given at one time
Monitor fibrinogen levels by clotting screens
How is blood donation regulated?
- EU Blood Safety Directive
- Blood Safety Quality Regulations
- Better Blood Transfusion 3
- MHRA inspections
- CPA inspections
What is haemovigilance?
Surveillance procedures covering entire blood transfusion chain:
Donation, processing of blood and its components, provision and transfusion to patients, and follow-up
What are haemovigilance SHOTs?
Serious Hazards of Transfusion (SHOT):
- Voluntary reporting
Report all Serious adverse Events (SAE) and Serious adverse reactions (SAR)
What are haemovigilance SABRE?
Serious Adverse Blood reactions and events (SABRE):
- Mandatory reporting
Report all SAR and SAE where the root cause error was the Quality system
