Blood transfusion Flashcards
What is a blood group system?
A blood group system is a collection of one or more RBC antigens under the control of a single gene or a cluster of closely linked homologous genes.
What are the most clinically significant blood groups?
ABO and Rh blood group systems.
What determines the clinical importance of a blood group?
Capacity of antibodies against the specific RBC antigens to cause haemolysis of RBC.
Why does your body produce ABO antibodies at a young age?
Sugars that are identical or similar to ABO antigens found in the food you eat stimulate the antibody production.
What class are ABO antibodies?
IgM.
What medical complications can and cannot occur due to ABO antibodies?
Acute HTRs through activation of the complement system resulting in massive intravascular haemolysis. However, they cannot cross the placenta to cause HDFN.
Why does haemolytic disease of the fetus and newborn (HDFN) happen?
Fetus has a different RBC antigen from mother. Antibody that corresponds to this antigen travels across placenta.
What genotype makeup is O blood group?
Recessive.
What genotype makeup is negative for D antigen?
Recessive.
What does the ABO gene code for?
An enzyme.
What do the RhD genes code for?
Antigen itself.
How can a RhD negative individual develop antibodies for RhD?
Transfusion of incompatible blood or if fetal RhD positive RBC’s enter maternal bloodstream.
What is alloimmunity?
Non self antigens from a member of the same species.
What class of antibodies are acquired alloantibodies?
IgG
Transfusion of incompatible RhD blood can lead to?
Delayed HTR - Extravascular haemolysis. Can result in high levels of bilirubin, jaundice or anaemia.
What does the A gene code for in ABO blood group?
An enzyme that add N-acetylgalactosamine to the H antigen.
What does the B gene code for in ABO blood group?
An enzyme that adds galactose to the H antigen.
What does an individual who has A and B alleles have on the red cell surface?
2 H antigens with A and B variants.
What does an individual who has both O alleles have on the red cell surface?
H antigen itself.
Apart from IgM being the main ABO antibody what other class is produced in small amounts?
IgG
Why do IgG ABO antibodies that cross the placenta not cause HDFN?
Fetal red cells have poorly developed ABO antigens which are unable to support binding of the IgG antibodies. ABO antigens are found on numerous other cells (not just red cells) so any IgG ABO antibodies that have crossed the placenta can be ‘mopped-up’ by these cells.
When can IgG ABO mediated HDFN occur?
Mothers who have especially high levels (‘high-titre’) of IgG anti-A and anti-B antibodies.
Why after a platelet transfusion anti-A or anti-B antibodies in the patient’s plasma causing destruction of the transfused platelets is unlikely?
Expression of ABO antigens on platelets is relatively low.
When transfusing platelets what is important?
Make sure it is high titre negative (doesn’t have high levels of anti A or anti B) or platelets of the same ABO group.
When transfusing FFP or cryoprecipitate what needs to be checked?
Antibodies. High titre negative or AB plasma (universal donor) or FFP/cryoprecipitate of the same ABO group
If you know a mother is RhD negative and has a fetus which is RhD positive what can be given to the mother?
Mother can be given anti d immunoglobulin to prevent alloimmunisation of RhD antibodies in her system which could lead to HDFN. Anti d immunoglobulin destroys any positive RhD fetal red blood cells that have entered maternal bloodstream.
What is the emergency blood type?
Group O RhD negative blood.
What RhD blood type can RhD positive individuals be given?
RhD positive or negative.
What RhD blood type can RhD negative individuals be given?
RhD negative only.
If platelets have been transfused of a different RhD type what can be given? Why does RhD group matter with platelets?
Anti-D immunoglobulin. Platelets can contain RhD red cells fragments.
In pre-transfusion compatability testing what is the forward group?
Patient red blood cells and reagents (antibodies).
In pre-transfusion compatability testing what is the reverse group?
Patient serum (patient antibodies) and red blood cells with know antigens.
When is an antibody screen test done?
To see if a patient has acquired alloantibodies.
How is an antibody screen test done?
Patient serum added to panels that contain red blood cells that have known antigens. Anti human globulin is added to visualise agglutination.
Why may anti-IgG be used?
To induce agglutination.
What is a cross match?
Patient serum mixed with sample of red blood cells chosen for transfusion.
What infection screening tests are done for blood?
HIV, Hepatitis (B,C,E), HTLV and syphillis.
How is HTLV screened for?
Antibody in blood.
How is syphillis screened for?
Antibody test.
What are the two ways to collect blood?
Whole blood donation and through an apheresis machine.
Advantage of collecting blood through an apheresis machine?
More of a specific blood component can be collected from one blood donor compared to whole blood donation.
Why is the blood component red cells refered to as ‘packed red cells’?
Most of the plasma has been removed. Red cells are suspended in a small volume of solution.
When would you transfuse red cells?
Anaemia (low haemoglobin) or blood loss.
What are platelets used to treat?
Thrombocytopenia, bleeding and platelet dysfunction (use of anti-platelet drugs).
Why are platelets in low supply?
Low shelf life (7 days). 4 Whole blood donations have to be pooled to get one unit of platelets.
What coagulation factors does FFP contain?
All coagulation factors.
What is FFP used to treat?
Bleeding, multiple clotting factor deficiencies, dilutional coagulopathy, disseminated intravascular coagulation.
What coagulation factors does cryoprecipitate contain?
Fibrinogen, factor VIII, VWF, factor XIII.
When is cryoprecipitate used?
To treat haemophilia A or VWF disease. Liver disease (low fibrinogen).
How are plasma derived medicines produced?
Thousands of plasma donations are pooled. Fractionated into different products.
What are the viral inactivation steps to produce plasma derived medicines?
Heat treatment and use of solvent detergent.
What is human albumin solution used to treat?
Low blood volume. Initiate diuresis in patients with low albumin.
What are the two types of immunoglobulin solutions?
Normal and specific.
What does normal immunoglobulin solution contain?
Immunoglobulins that correspond to common viruses in the population.
What does specific immunoglobulin solution contain?
High levels of antibody for specific target.
Why are prothrombin complex concentrates better for treating patients with major bleeding than FFP?
Administering PCCs takes less time than FFP as FFP needs to be thawed.
What is a major haemorrhage defined as?
Blood loss of >30% circulating blood volume
In situations where there is massive bleeding patients can develop coagulopathy as a result of?
Dilutional coagulopathy or consumptive coagulopathy.
What is dilutional coagulopathy?
If large volumes of red cells and other fluids (e.g. saline) that contain no coagulation factors or platelets are transfused.
What is consumptive coagulopathy?
Due to depletion of coagulation factors as haemostasis is activated.
How to avoid dilutional coagulopathy?
Transfusing red cells and FPP in either a 1:1 or 1:2 ratio (1 FFP for every 2 units of red cells given).
Why is there no risk of harm immediately following mistransfusion of RhD blood?
Anti-D antibodies usually become apparent 2 to 5 months after the exposure – so there is no risk of harm (HTR) .
