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.