Blood transfusion Flashcards
What is a blood group system?
Collection of one or more RBC antigens under the control of a single gene or a cluster of closely linked homologous genes
When are antibodies against RBCs clinically significant?
When they can cause haemolysis resulting in…
- haemolytic transfusion reactions
- Haemolytic disease of the foetus and new born (when foetus has a different RBC to mother and mother produced an antibody to it which crossed the plasma
Name the two types of antibodies against RBC antigens
Naturally occurring antibodies
Acquired alloantibodies
What are naturally occurring antibodies?
production of antibodies stimulated by encounters with the missing antigens in food groups or microorganisms - happens at an early age
Usually IgM and remain IgM - can cause HTRs but cannot cross placenta to cause HDFN
*easy agglutination allowing easy blood grouping
What are acquired alloantibodies?
Formed as a result of active immunisation following exposure to non-self RBC antigens in other individuals
Arise due to incompatible blood transfusions (eg RhD positive transfused to RhD negative) or in pregnancy when fetal RBCs can enter maternal blood system
Usually IgG antibodies - do not cause massive HTR but can still cause haemolysis leading to delayed HTRS
Can cross the placenta and cause HDFN
What antigen does a group A RBC have and what antibody is in the plasma?
A-antigen
This anti-B antibodies
What antigen does a group B RBC have and what antibody is in the plasma?
B-antigen
Thus anti-A antibodies
What antigen does a group AB RBC have and what antibody is in the plasma?
Both A and B antigens thus no antibodies
What antigen does a group O RBC have and what antibody is in the plasma?
No antigens
this anti-A and anti-B antibodies
Why do IgM ABO antibodies cause potentially fatal haemolysis
They are capable of fully activating complement
Why do the rare IgG ABO antibodies in plasma not cause HDFN?
Poorly developed ABO antigens so the IgG antibody cannot bind
ABO antigens found on numerous other cells so can be mopped up by binding to those cells instead
Any present in the babies plasma disappear within a few months as they develop their own IgM anti-A and anti-B antibodies
What antigen and antibody to D positive patients have?
D antigen
No antibodies present
What antigen and antibody to D negative patients have?
No antigen
Can develop anti-D antibody if exposed to D positive red blood cells
What can anti-D antibodies cause?
Delayed HTRs - due to extravascular haemolysis often due to transfusions leading to anaemia, jaundice etc
HDFN - severity can vary but can cause either brain damage due to high bilirubin or intra-uterine death
How do you stop pregnant RhD negative women from developing anti-D antibodies?
Given anti-D immunoglobulin which destroys any RhD positive fetal RBCs entering the mothers circulation before she forms her own anti-D antibodies