Transfusions Flashcards
What is the minimum criteria for men and women to donate blood?
Hb >135g/L in men Hb >125g/L in women Weight over 50kg
Blood samples from patients for G&S undergo microbiological testing, what does this look for?
HIV, Hep C, Hep B, HTLV, syphilis
How long are red cells, FFP and platelets stored respectively?
Red cells = 35 days at 4 degrees FFP = 3 years at -30 degrees Platelets = 7 days with agitation at 22 degrees
What is made available at the transfusion lab?
Blood components - red cells, FFP, platelets, cryoprecipitate Blood products - anti-immunoglobulin, prothrombin complex concentrate Blood products from pharmacy - IV Ig, human albumin, specific Ig
Where is the gene for the ABO grouping system found?
Chromosome 9
What do A and B genes code for?
Transferases which modify a precursor called H substance on red cell membranes
In the ABO system, which is dominant?
A and B are dominant over O A and B are co-dominant O is silent
What are the potential genotypes for each group phenotype e.g. group O etc.
Group O - OO Group A - AA or AO Group B - BB or BO Group AB - AB
How is your ABO group inherited?
One ABO gene from each parent
What is Landsteiner’s law?
When an individual lacks the A or B antigen the corresponding antibody is produced in their plasma Naturally occurring antibodies cause haemolysis of red cells expressing the specific antigen
According to Landsteiner’s law, which antigen and antibody will a person with ABO group A, B, AB and O have respectively?
A - antigen A, anti-B B - antigen B, anti-A AB - antigen A and B, no antibody O - no antigen, anti-A and anti-B
What is the next most important antigen after A and B?
RhD 85% of population are RhD positive
How is RhD inherited?
2 alleles D and d, inherit one from each parent
What can anti-D antibody cause?
Transfusion reactions and haemolytic disease of the foetus and newborn
What should be avoided in RhD negative people?
Exposure to D antigen through transfusion i.e. RhD negative blood to RhD negative people
Why are other blood group systems (other than ABO and Rh systems) not as important?
Not as immunogenic
Why is pre-transfusion testing important?
Allows identification of ABO and RhD group of patient and presence of clinically significant red cell antibodies i.e. allows selection of appropriate blood for transfusion
What is used to identify antigens present on the red cell?
Antisera - a reagent with known antibody specificity
What is used to identify antibodies present in the plasma?
Reagent red cells - red cells with known antigen specificity
What happens when the antigen on red cells reacts with the antibody specific for antigen of interest?
Agglutination of red cells
How is a patient’s ABO blood group identified?
Test patients red cells with anti-A, anti-B and anti-D antisera IgM reagents - direct agglutination i.e. if test is positive they have the antigen
What does an IAT crossmatch check for?
Agglutination indicates donor cells are incompatible with patient plasma. No agglutination means cells can be issued for transfusion
What are some indications for red cell transfusion
Symptomatic anaemia, Hb<70g/L or 80g/L if cardiac disease Major bleeding
How many units of red cells are transfused at a time?
1 unit initially and reassess
What are some indications for platelet transfusion?
Prophylaxis in patients with bone marrow failure and very low platelet counts. Treatment of bleeding in thrombocytopenic patient. Prophylaxis prior to surgery/procedure in thrombocytopenic patient
What are some indications for fresh frozen plasma (FFP) transfusion?
Treatment of bleeding in patient with coagulopathy (PT ratio>1.5), prophylaxis prior to surgery or procedure in patient with coagulopathy, management of masssive haemorrhage, transfuse early in trauma
When are patient’s obs done during transfusion?
Before blood is commenced, at 15 minute intervals and within 60 minutes of completion
What are the signs and symptoms of acute transfusion reaction?
Symptoms - chills, rigors, rash, flushing, feeling of impending doom, collpase, loin pain, resp distress
Signs - fever, tachycardia, hypotension
What is the pathophysiology behind AHTR?
Binding of IgM anti-A or anti-B antibodies to their corresponding antigen leads to complement activation and lysis of transfused cells
Release of inflammatory cytokines:
- Complement, kinin and coagulation systems all activated
- Shock, increased vascular permeability, disseminated intravascular coagulation, renal failure
- Often fatal
How would the transfusion lab manage an AHTR?
- Repeat ABO and RhD group of pre and post transfusion samples - Is there a discrepancy?
- Direct antiglobulin test - is there antibody bound to donor cells?
- Repeat crossmatch - Are the donor unit(s) incompatible?
- Send remains of unit for culture
What are the clinical features and risk factors associated with transfusion associated circulatory overload?
Clinical features - respiratory distress, hypertension, raised JVP, positive fluid balance
Risk factors - elderly, cardiac failure, low albumin, renal impairment, fluid overload
How is transfusion associated circulatory overload managed?
Oxygen, supportive care and diuretics
What is a delayed haemolytic transfusion reaction?
- Patient mounts delayed immune response to red cell antigen- usually IgG
- Positive DAT
- Extravascular haemolysis 5-10 days post transfusion
- Transfused cells destroyed
- Hb may drop, raised bili, LDH
- Positive DAT and detection of alloantibody
