Haem - Blood transfusion Flashcards
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
Why can we not reply on infection testing donor blood?
Test for infections cannot pick up all infections, especially those that are not detectable in early stages
so only give to those who need it
What is Prion disease?
Normally - Prion protein found in membrane of lymphocyte & platelet
Prions of variant Creutzfeldt-Jacob disease (CJD) found in lymphoreticular tissues
(4 cases by blood transfusion - test is not available)
What are the infections tested on donor?
HIV
Hepatitis B,C,E
HTLV
Syphilis
Others:
CMV (cytomegalovirus)
T. Cruzii
Malaria
