Haem - transfusion Flashcards
What are the ABO and Rhesus blood group systems?
They are examples of and the most important groups of RBC surface antigens which identify the RBC to the immune system.
How many RBC antigen systems are there and what are these antigens
At least 30
The antigens are polypeptides, polysaccharides or glycoproteins.
Name the minor blood group systems
Kell MNS Lewis P Duffy
What is the H antigen
All patient’s RBC’s have a ‘core antigen’ called the H antigen. The H antigen is a disaccharide.
Describe the ABO system
Group O
- the patient’s only express the H antigen. O signifies no other sugars are added
Group A
- Additional CHO group N - acetylgalactosamine is bound to H antigen making a trisaccharide = The A antigen
Group B
- D-glacatose is bound to the H-antigen –> making a trisaccharide = the B-antigen
Group AB
- These patients express both A and B antigens
What is the Rhesus blood group named after
The Rhesus monkey, the animal whose blood was used in discovery of the Rhesus system
How many different Rhesus antigens are there and which are the most important. Which rhesus antigen is present when patients are referred to as Rhesus positive?
50
Most NB D C c E e
D is most NB. This is the antigen present in patient’s who are referred to as Rhesus positive.
What is the Rhesus D antigen
A large (30 Da) cell membrane protein, thought to be a subunit of the NH3 transport protein. Genetics determine the presence of this Ag on the RBC surface.
85% population are Rhesus D positive
What percentage of population is Rhesus negative
± 15%
Why does the immune system develop antibodies to non-self red cell antigens
- Exposure to foreign RBCs
- Placental abruption
- Blood transfusion - Exposure to environmental antigens (e.g. food / bacteria) –> may be similar to nonself RBC Ag with cross reaction.
Antigen Presenting Cells (APCs) present foreign material to the immune system which then develops antibodies.
At what age are non-self ABO Ag present in the plasma. What antibodies are produced by each blood group
From 6 months onwards (environmental Ag that have a similar chemical structure to ABO Ags)
Group O - Anti A and Anti B
Group A - Anti B
Group B - Anti A
Group AB - none
What type of antibodies are Anti A and Anti B and why is this important.
IgM
This is important as IgM is unable to cross the placenta –> if it could every fetus of different blood group to the mother would have its RBCs attacked by maternal immune system.
How does the development of non-self antibodies differ between the ABO blood group system and the Rhesus blood group system
The 15% of the population who are RhD negative DO NOT naturally develop RhD antibodies. Anti-RhD antibodies are only acquired on exposure to foreign RBCs carrying the RhD Ag.
When can exposure to the RhD antigen occur (i.e. in a Rh negative patient)
- incompatible blood transfusion - RhD pos blood into RhD neg patient
- Fetal-maternal haemorrhage
- After childbirth/abortion/trauma/placental abruption
- If Rh pos fetus and Rh neg mom –> the maternal immune system will then develop anti-RhD antibodies which are IgG and are able to cross the placenta
What type of Antibodies are Anti-RhD and why is this important
IgG
This is important as these antibodies DO cross the placenta. Current and future fetuses can develop haemolysis and severe anaemia and if they survive to term will be born with haemolytic disease of the newborn.
What is RhoGAM?
“rhod Immune globulin human”
This is anti-RhD immunglobulin given to mothers once or twice during pregnancy and at birth in an attempt to prevent maternal sensitization to RhD.
The parenteral anti-RhD IgG binds and removes any fetal RBCs which pass into the maternal circulation.
What is allogenic versus autologous blood transfusion?
Allogenic - donor blood (usually packed red cells) is given intravenously to a recipient
Autologous blood transfusion is where blood is taken from a patient and re-infused back into the same patient when required.
Examples:
1. Intra-operative cell salvage
2. Preoperative autologous blood donation
3. Acute normovolaemic haemodilution
Give three examples of autologous blood transfusion
Examples:
- Intra-operative cell salvage
- Preoperative autologous blood donation
- Acute normovolaemic haemodilution
When will a haemolytic transfusion reaction occur. What is the mechanism of this?
When the recipients blood contains antibodies to the donor’s RBC antigens.
Recipient antibodies coat the donor RBCs. The Ab-Ag complex activates the complement cascade –> haemolysis of donor RBCs.
What are the two types of haemolytic transfusion reactions. Describe and differentiate these types.
IMMEDIATE (within 24 hours) –> usually first 6 hours
- ABO
- Complement
- Intravascular haemolysis
- Severity depends on Ab titre
- Clinically: Uritcaria / flushing / chest pain / dyspnoea / jaundice / tachycardia / shock / Hburia / DIC
- If RhD –> extravascular haemolysis + less severe
DELAYED (After 24 hours –> usually 7 - 21 days up to 30 days)
- Minor RhD antigens and the minor blood group systems (Kell, Lews, MNS, P and Duffy)
- Ag exposure –> secondary immune response –> formation of IgG (which takes a few days –> hence the delay.
Why is delayed haemolytic reaction ‘delayed’
Exposure of patient blood/immune system to minor blood group antigens elicits a secondary immune response with the production of IgG antibodies. Therefore, there is a delay as the antibodies take time to be made
Define Universal Donor and universal recipient
Donor: Group: O negative
Recipient: AB positive
What is a cross match? What are the different types of cross match that can be performed
Compatibility test between donor and recipient blood
Major cross match
- Donor RBCs mixed with recipient plasma –> if clumping then blood is incompatible
Minor cross match
- Recipient RBCs mixed with donor plasma
Why is minor cross match no longer frequently performed
RBCs are now transfused as packed cells and thus contain an insignificant amount of donor plasma.
Minor cross match = recipient RBCs with donor plasma
How are Packed RBCs made and stored
- Cetrifuged whole blood –> plasma removed
- RBCs resuspended in minimum amount of fluid Hct > 75%
- Citrate, Adenine and glucose added
- Storage at 4 degrees
- Shelf life 42 days
What changes occur to RBCs during storage
- Some become spherical (reduced life span)
- K+ rises to 30 mmol/L by 28 days
- ATP levels fall
- 2.3-DPG fall (after transfusion it takes 24 hours for 2,3-DPG levels to return to normal)
How long does it take 2,3 DPG levels to return to normal after a unit of packed red blood cells is transfused and what theoretical and clinical implications of this are there
24 hours.
Low 2,3-DPG means Hb in relaxed state with higher affinity for O2 than native Hb. This means it is less likely to offload the O2 to the tissues (The P50 of the OHDC is shifted to the left).
It is still unclear if this has any clinical/practical implications with regards to O2 delivery in the patient immediately after a blood transfusion.
What is FFP. How is it produced and stored? What is FFP shelf life
Fresh Frozen Plasma.
This is the plasma removed from whole blood during the process of producing packed RBCs.
Storage
1. Cooled to -30 deg C within 8 hours of donation
Shelf life
1. 1 year
What is FFP used for
- To replace coagulation factors
2. To derive other blood products
What other products can be produced from FFPs. Describe these products
- Cryoprecipitate
- FFPs to -70 deg C –> thawed + centrifuged –> precipitate collected
- Rich in factors: Fibrinogen (1), 8, vWF, 13 - Freeze-dried factor 8 concentrate
- small amount of fibrinogen
- used in haemophilia A - Freeze-dried factor 9 concentrate
- small amount: fibrinogen, 2, 7, 10
- Used in Christmas disease (Haemophilia B - IX deficient)
How are platelets produced
Either pooled platelets or from multiple donors or collected from one donor.
Process is apheresis (machine)
How is risk of infectious disease in platelets mitigated
Ultraviolet irradiated
How are platelets stored? What is their shelf life
At room temperature –> become non-functional at 4 deg C.
shelf life: 5 days
Can platelets be transfused without cross match
Yes but the platelet count rises more if they are ABO type specific
What is cell salvage
Method of autologous blood transfusion: patient’s own blood is collected, processed, stored and re-transfused
NB to reduce need for allogenic transfusion
Red cells are collected from surgical field then centrifuged, washed and resuspended in saline
What are the advantages and disadvantages of cell salvage?
Advantages
- More cost effective
- No infective / immune risk
- Accepted by some Jehovahs witnesses
Disadvantages
- Electrolyte abnormalities (esp. in massive t/f)
- Clotting factors lost –> dilutional coagulopathy
- Precipitate amnioitic fluid embolus (not completely removed by washing process)
- Cancer cells
How can the risk of precipitating amniotic fluid embolus / cancer cell reinfusion with cell salvage be reduced and considered safe
Combining cell salvage with a leucocyte depletion filter
What is a massive transfusion
Transfusion of more than the patients circulating blood volume < 24 hours
OR
Transfusion of more than half patient’s blood volume in < 4 hours
What are the additional risks conferred by MASSIVE transfusion
- Hypothermia (causing: coagulalopathy / arrhythmia / Left OHDC)
- Dilutional coagulopathy
- Hypocalcaemia (citrate)
- Hyperkalaemia (K = 30 mmol/L at day 28)
- Acidosis (pH 6.8) –> lactate accumulation due to anaerobic metabolism of RBCs during storage
What is the role of citrate in stored blood
To chelate Ca++ to prevent coagulation of stored blood
What are the alternatives to using blood for O2 carriage?
- Hb-based O2 carriers
- Hb cross linked polymerized and encapsulated (Hb alone causes renal tubular damage) - Perfluorocarbon based O2 carriers
What are the advantages to using O2 carrying blood substitutes over human blood
- Infection/immune complications
- Longer shelf life
- Stored at ambient temp
- Acceptable to Jehovah’s witnesses
