Haem - Blood transfusion Flashcards
(27 cards)
What are the 4 blood groups and what antibodies do they have respectively?
A - anti-B
B - anti-A
AB - none
O - anti-A/anti-B
What characteristics are there of blood antibodies?
- Present from birth
- IgM class
- Capable of fully activating complement - fatal haemolysis if mixed transfusion
How are A/B antigen formed?
Sugar residue on common glycoprotein & fucose stem (H antigen)
A - galnuc
B - gal
O - N/A
How are antigens determined?
Gene code for:
A - enzyme to add N-acetyl galactosamine
B - enzyme to add galactose
What is the genetic pattern of ABO genes?
AB co-dominant
O recessive
How is a blood transfusion deemed incompatible?
If there is agglutination of Abs and anti-Abs
Why is O- group blood available to everyone?
It has no antigens
What and how are components of the blood split?
Centrifuge (top - plasma, middle - platelets, bottom - RBC) and squeeze into satellite bags
What can plasma function be further split into?
- FFP (fresh frozen plasma)
- Cryoprecipitate
- Plasma for fractionation - Albumin//factorVIII: XI immunoglobulins, anti-D etc.
Where is blood collected from donor?
Collected into sterile bags containing anti-coagulant
Why is it not efficient to use whole blood to transfuse patients?
Patients only need some components, can risk excess fluid overload eg anaemia
- less waste of valuable resource
What is one unit of blood?
Whole blood derived from single donation
What is the Rh system?
Antigen D - where Rh D negative means no D antigen & vice versa
What are the genotypes of blood groups?
A: AA/AO
B: BB/BO
AB: AB
O: OO
What are the genotypes of +ve & -ve RhD?
+ve: Dd/DD
-ve: dd
Why must sensitisation (exposure to D antigen) be avoided?
To avoid creating anti-D in RhD negative people
How can sensitisation (exposure to D antigen) be avoided?
- Transfuse blood with same RhD
- Use O- blood
How can sensitisation happen and what implications does it bring?
Transfusion
-Future +ve transfusion can react to cause “delayed haemolytic transfusion reaction”
Pregnancy (mother -/foetus+)
- 2nd pregnancy - Mother IgG anti-D Abs cross placenta to cause haemolysis of foetal RBC - “Haemolytic disease of the newborn”
How does the severity of “Haemolytic disease of the newborn” HDN determine the baby’s fate?
- Not severe: Baby survives with high bilirubin levels –> brain damage/death
- Severe: Hydrops fetalis –> death
Why can mother anti-D Abs cross placenta?
It is of IgG class, only they can cross
What other RBC antigens are there?
Dozens more (Eg Cc Ee Kell Duffy Kidd) but only 8% form antibody - those need to use corresponding negative blood or risk delayed haemolytic reaction
How to we test patient before transfusion?
- Compatibility test - antibody screen on patient plasma (incubated with 2/3 different fully “screening” RBC) to exclude clinically significant immune antibodies
- if -ve, any blood given
- if +ve, identify antibody using panel
- -> select donor - Cross match - patient serum mixed with chosen RBD donor
- -> should not react
What blood donors are excluded?
- Risk to oneself (cardiovascular/neurological disease)
- Risk to others (infections, drugs, blood-borne diseases [early stage not yet detectable])
What are the two tests done on donor blood?
- Grouping and screening - test to ensure no strong clinically significant RBC abs are in donor plasma other than ABO groups
- Infection testing
- but cannot pick up all infections
