Blood Transfusions 1 Flashcards
What determines ABO blood groups (2)
Antigens on the red cell membrane (these antigens are sugars)
The naturally-occuring antibodies in the plasma (these antibodies are IgM)
What does ABO incompatible blood transfusion cause
Massive intravascular haemolysis - potentially fatal
Group A antibodies present
Anti-B
Group B antibodies present
Anti-A
Group AB antibodies present
None
Group O antibodies present
Anti-A and Anti-B
Group A antigens present
A antigen
Group B antigens present
Group B
Group AB antigens present
A and B antigens
Group O antigens present
None
Red cells which carry the RhD antigen
RhD positive
What do RhD negative patients lack
RhD antigen
These patients make immune anti-D if exposed to RhD positive red cells
Immune anti-D antibodies are IgG, which do not cause direct agglutination of RBCs - no immediate haemolysis and death, but delayed haemolytic transfusion reaction
Who can get RhD negative blood
Anyone
What can occur if RhD positive blood is given to a RhD negative patient
Form anti-D - RhD negative blood would be an issue in any future transfusions
Why is RhD antigen relevant
Immune Anti-D made by a Rh negative mother exposed to Rh positive blood, can cause haemolytic disease of the newborn or severe fetal anaemia and heart-failure (hydrops fetalis) in RhD-negative females of child bearing potential.
What percentage of the population are RhD positive
85% are RhD positive
15% are RhD negative
What is tested before transfusion (2)
ABO and RhD group
What Ig are immune antibodies
IgG
How many RBC antigens are there
100s, but the most important are A, B and D
How are RBC antibodies created (2)
As a result of transfusion and/or pregnancy
Why must we identify clinically significant RBC antibodies and transfuse RBCs that are negative for that antigen
To prevent a delayed haemolytic transfusion reaction
Where does a delayed haemolytic transfusion reaction occur
Spleen
Where are RBC antigens present
Expressed on RBC membrane
How are patients plasmas screen for IgG antibodies
By mixing with 2 or 3 reagent cells that, between them, express all the important red cell antigens. These reagent red cells are blood group O.
What technique is used for antibody screening for plasma
Indirect antiglobulin technique
What is IAT (indirect antiglobulin technique)
Low ionic strength saline brings the cells closer together and the mixture is incubated at 37 degrees.
Bridges red cells coated by IgG which cannot themselves bridge 2 red cells - to form a visible clump - takes 30mins incubation at 37 degrees.
When is an antibody screen done
Before every transfusion, even if it has been done before
What is G&S
Group and Screen
What will happen if there is an immune antibody during the antibody screen
The red cells will clump - positive screen.
How is blood grouping and antibody screening automated (6)
Bar coded samples (id correct throughout – no mix up)
Computer interfaces
Robotic sample and reagent handling
Liquid level sensors (? failed to add reagent)
Reading of results by image analysis
Interpretation of results
Download to patient record
Why is automation of blood grouping and antibody screen good
No manual steps = safer and quicker
What cell panels are used to identify RBC antibodies
10 cell panel
What is donor blood labelled with (4)
ABO and D type
Other Rh antigens and K
Who is given K negative blood for transfusion
Females of childbearing potential
What is HDFN
Haemolytic disease of the foetus and newborn
Why is it important to given females of childbearing age K negative blood
Anti-K can cause haemolytic disease of the newborn
What proportion of the population is K negative
85-90%
What is the next step after ABO and Rh status is matched
Serological crossmatch
What is the serological cross match for
Detects any antibody:antigen reactions between the donor and recipient blood
What are the two forms of serological crossmatch and what is involved in each.
Full crossmatch - indirect antiglobulin technique. Patient plasma is incubated for 30-40 mins, will pick up antibody antigen reaction that could cause destruction of the red cells and cause extravascular haemolysis
Add antiglobin reagent.
Immediate spin (saline, room temperature) - incubate patient plasma and donor red cells for 5 mins only and spin, will detect ABO incompatibility only
What are the drawbacks of immediate spin for serological testing
Will only detect ABO incompatibility and used in an emergency to detect if the right ABO group has been selected.
This prevents an immediate, but not delayed haemolytic transfusion reaction.
What is electronic crossmatching of blood
If we have tested the patient’s blood group twice (and it is the same) and the recent antibody screen is negative we can select blood without doing any mixing.
What are the benefits of electronic crossmatching of blood (5)
This only takes a few minutes
There has to be a computer algorithm in place and it should be set up to prevent incompatible blood being issued
Blood is only issued when it is needed and it is quicker. It also means that all the blood is in the stock fridge, not assigned to a patient. We can even release blood from a fridge on another site – this is called remote issue.
When might electronic crossmatching be unsuitable (3)
Some patients are not suitable for electronic crossmatching – those with anomalous blood groups, those with red cell antibodies and those who have only had a blood group tested once.
What approach is used in clinical transfusion practice
Patient blood management is the modern approach to clinical transfusion practice.
You should remember this whenever you consider whether transfusion is needed.
It is the same as any other treatment decision. And must involve the patient.
What needs to be considered when deciding whether a patient needs a blood transfusion (6)
Is the patient bleeding? What are the blood results? Is the patient symptomatic? Will a transfusion solve the problem? What are the risks of transfusion? Are there alternative treatments?
What is the importance of patient consent with blood transfusions (4)
‘Valid’ consent is required for transfusion (verbal)#
Alternatives should be offered if appropriate
If transfused in an emergency, patient must be informed afterwards
Involve patients in the process to ensure they get the right blood and the right ‘special requirements’
What is the lifespan of red cells for transfusion (3)
Stored at 4 degrees for 35 days.
Must be transfused within 4 hours of leaving fridge
Transfer 1 unit RBC over 2-3 hours
What is the lifespan of platelets for transfusion (2)
Stored at 22 degrees for 7 days
Transfuse 1 unit of platelets over 20-30 minutes
What is the lifespan of plasma for transfusion (2)
No need to crossmatch, but does need 30-40mins to thaw
Transfuse 1 unit over 20-30 mins.
What warrants RBC transfusions (4)
Major blood loss - if >30% blood volume lost
Per-op, critical care - Hb <70g/L versus 80g/L
Post chemo: Hb<80g/L
Symptomatic anaemia - ischaemic heart disease, breathlessness, ECG changes
How often should the Hb be checked when transfusing RBCs
Pre transfusion and after every 1-2 units
Transfusion to above 100g/L is rarely required, unless symptomatic or severe cardiac/respiratory disease, etc…
What effect does 1 unit of RBC have on Hb
1 unit RBC gives a Hb increment of 10g/L in a 70-80kg patient
What is the maximum surgical blood ordering schedule (MSBOS)
Red cells often allocated to a patient but, if not used, are taken
back into stock…repeatedly, may expire.
So, MSBOS is based on negotiation between surgeons and
transfusion lab about predictable blood loss for ‘routine’ planned
Surgery.
Some operations rarely need blood - eg: gall bladder op
Some operations always need blood – eg: aortic aneurysm repair
Junior doctors / nurses doing pre-admission clinics have some idea
what is normal. Have to be flexible if non-standard surgery or
special patient requirements (eg: bleeding disorder)
What steps are required RE blood preparation pre elective procedures (2)
Group and Screen (and save) - then if no antibodies present, do not cross-match blood, but just save sample in the fridge (if unexpected need for blood, can provide it within 10mins (by electronic issue, as no anti bodies present)
Always crossmatch up front if RBC antibodies are present
How is a patients own blood used during surgery (3)
Cannot use pre-operative autologous deposit (i.e. donate own blood before operation)
Intra-operative cell salvage - collect blood lost during surgery, centrifuge, filter, wash and re-infuse it. Used in most surgical and obstetrics units
Post-operative cell salvage - collect blood lost post-op into wound drain, filter and re-infuse. mainly used in orthopaedic surgery (i.e. knee)
What is in cell salvage blood
All coagulation factors and platelets are removed
Autologous
Own
Allogeneic
Donor
When is CMV negative blood required
Only required for intra-uterine and neonatal transfusions (new guidance 2012). Also for elective transfusion in pregnant women (baby in-utero is exposed to maternal transfusion)
What are some special requirements for blood transfusion (3)
CMV negative
Irradiated blood
Washed
When is irradiated blood required for transfusion
Required for highly immunosupressed patients, who cannot destroy incoming donor lymphocytes: which can cause (fatal) transfusion associated graft versus host disease (TA-GvHD)
When is washed blood required for transfusion
Red cells and platelets are only given to patients who have severe allergic reactions to some donors’ plasma proteins
When is platelet transfusion contra-indicated (2)
Platelet transfusion is contraindicated in heparin-induced thrombocytopenia (HIT) and TTP (can worsen)
By how much does 1 unit of platelets raise platelet count
30-40 x 10^9/L
What is the indication for a massive platelet transfusion
Aim for platelets >75 x 10^9/L
When are platelets transfused post-chemo
If <10x 10^9/L (or <20 if sepsis)
When are platelets transfused to prevent surgical bleeding
<50 x 10^9/L (of <100 if critical site such as CNS or eyes)
When are platelets indicated in platelet dysfunction or immune causes
Only if there is active bleeding
What is FFP
Fresh frozen plasma containing all clotting factors
What is the adult dose of FFP
15mL/kg
1 unit FFP contails 250ml = adult dose is 4-6 un its.
What is the treatment of choice to reverse warfarin
PCC (prothrombin complex concentrate)
When is platelet transfusion indicated (4)
Massive transfusion
Prevent bleeding post-chemo
Prevent bleeding - surgery
Platelet dysfunction or immune cause
What are the FFP transfusion indications (4)
Massive transfusion
Disseminated intravascular coagulopathy (DIC)
Liver disease and risk
Rarely for coagulation factor replacement where factor concentrate not available
When is a massive FFP transfusion indicated
Blood loss >150ml/min
When should you give FFP in DIC
WITH active bleeding
When should you give FFP in liver disease
PT ratio >1.5 x normal
