Approximately how much blood is taken off from donor and by what technique?
Approximately 300ml blood
gravity venesection
Who is Karl Landsteiner?
Austrian-born American physician
Recognised the problem of blood incompatibility
Identified agglutinins in the blood
Distinguished main blood groups
Father of transfusion medicine: Nobel prize - 1930
What are the significance of blood groups?
Red cells have antigens on their surface
Human plasma may contain antibodies to these antigens
These can cause reactions - sometimes fatal
This is the fundamental problem in blood transfusion
What are agglutinins?
Naturally occurring (pentameric) IgM antibodies
What does transfusion of ABO incompatible blood cause?
intravascular lysis of red cells
This can lead to a major life-threatening transfusion reaction causing:
shock, hypotension, tachycardia
renal failure, loin pain, haemoglobinuria
disseminated intravascular coagulation
death
Why do we have ABO antibodies?
Antibodies to ABO antigens occur naturally due to cross reactivity with gut bacterial antigens
These are IgM (pentameric) antibodies able to fix complement and cause red cell lysis
What antigens and antibodies do people with blood group A have?
Antigen on RBC surface: A
Antibody in plasma: Anti-B
What antigens and antibodies do people with blood group B have?
Antigen on RBC surface: B
Antibody in plasma: Anti-A
What antigens and antibodies do people with blood group AB have?
Antigen on RBC surface: A and B
Antibody in plasma: none
What antigens and antibodies do people with blood group O have?
Antigen on RBC surface: none
Antibody in plasma: Anti-A & Anti-B
What is the Forward grouping reaction?
Washed red cells from the patient are mixed with anti-A or anti-B antibody
Eg this is blood group A
What is the reverse grouping reaction?
patient serum is mixed with known red blood cells to detect antibodies
How does cross-matching work?
Forward grouping (detects antigen)
Reverse grouping (detects antibody)
How does blood grouping with gel cards work?
POSITIVE RESULT: if blood is at top of column (agglutination reaction)
test for antigens: patients RBCs +:
anti-A antibody
Anti-B antibody
anti-D antibody (Rhesus - gives + / -)
control: patient RBCs + patient plasma
test for antibodies: patient Plasma +:
A RBCs
B RBCs
Plasma + B RBCs
What blood group is protective for COVID 19?
O
What blood group is at higher risk for COVID 19?
A
What is 'group and screen'?
Test the ABO group of the red cells
Screen the plasma for “atypical antibodies"
What are atypical antibodies?
arise due to sensitisation with foreign red cell antigens caused either by:
previous blood transfusion or
by pregnancy
Atypical antibodies can cause blood transfusion reactions if the patient is transfused with incompatible blood in the future
What is the Coombs test?
also known as the anti-globulin test
anti-immunoglobulin antibody to agglutinate red cells
two types:
direct (DAT): whether red cells are coated with antibody
indirect (IAT): whether a patient is positive for Rhesus and other blood groups
When is DAT (direct anti-globulin test) positive?
after a transfusion reaction and in HDN (haemolytic diseaes of newborn) (allo-antibodies)
in autoimmune haemolytic anaemia (auto-antibodies)
What is the Rhesus system?
Test for Rh antigen
Rh positive people cannot develop anti-D antibodies
What is Rhesus sensitisation?
Rh -ve people can develop antibodies if they are transfused with Rh +ve blood or are pregnant with a Rh +ve baby
the antibody generated is IgG type
What is haemolytic disease of the newborn (HDN)?
If an Rh -ive mother is pregnant with an Rh +ve fetus, she may produce antibodies that can cross the placenta and harm the baby
can cause anaemia, jaundice and kernicterus (braindamage)
How is HDN prevented?
Pregnant women have the ABO and Rh blood groups checked at 12 weeks’ booking
Rh -ve women (15%) receive anti-D antibody i.m. injection at 28 weeks’ gestation to prevent sensitisation
Baby tested at birth and if Rh +ve then the mother receives further anti-D until Kleihauer test for fetal cells in the maternal circulation becomes negative
If previously sensitised, then subsequent pregnancies require monitoring via trans-cranial Doppler scan and may require intra-uterine transfusions if signs of anaemia are severe
What is in a bag of donated blood?
Red cells
Buffy coat:
white cells
platelets
Plasma:
albumin
gamma globulins
coagulation factors
Water, electrolytes, additives
What is Apheresis?
separates donated blood components
Platelets are pooled from 4 donors to produce single unit
Apheresis can produce a single unit from one donor
When to give a blood transfusion?
Severe acute blood loss:
Severe trauma e.g., road traffic accident
Massive GI blood loss
Obstetric blood loss
Elective surgery associated with significant blood loss
Medical transfusions:
Cancer, chemotherapy, renal failure
Anaemia:
Only for symptomatic anaemia or if refractory to haematinic replacement
Bone marrow failure e.g., myelodysplasia or aplastic anaemia
Haemoglobinopathy - thalassaemia major and sickle cell disease
What type of transfusion?
Blood components: Red cells, Platelets, Fresh frozen plasma, Cryoprecipitate (fibrinogen)