Blood Transfusion Flashcards
Why is the ABO system so important?
We have naturally occurring antibodies against any antigen NOT present on our own cells
The antibodies are reactive at 37degrees and can cause potentially fatal haemolysis
How are A and B antigens formed?
Adding a sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane
What does groups O consist of?
H stem only
Neither A or B sugars
How are antigens determined?
Corresponding genes
What does the A gene code for?
An enzyme the adds N-acetyl galactosamine to the common H antigen
Co-dominant
What does the B gene code for?
An enzyme that adds galactose
Co-dominant
Why is group O safe to give in an emergency?
No ABO antigens
What are the features of the Rh system?
Most important antigen is D
Blood groups: RhD positive (have the D antigen) or RhD negative
What are the genes for the RhD group?
D gene oceans for D antigen on red cell membrane
d gene codes for no antigen and is recessive (no actual antigen)
What are the possible genotypes for RhD?
Positive- DD or Dd
Negative- dd
When is it possible for RhD negative people to make anti-D antibodies?
After exposure to the RhD antigen
Either by transfusion of RhD positive blood
Or if a woman is pregnant with a RhD positive foetus
What are the implication of anti-D antibodies?
Future transfusion must have RhD negative blood
Can cause HDN (haemolytic disease of the newborn)
How is HDN caused?
If a RhD negative mother has anti-D from first pregnancy
In next pregnancy, if the foetus is RhD positive, the mothers anti-D antibodies can cross the placenta
Attach to the RhD positive red cells and cause haemolysis of foetal red cells
What can severe HDN cause?
Hydrops fetalis and death
What can less-severe HDN cause?
The baby survives but after both the high bilirubin levels can cause brain damage or death
How can sensitisation of RhD negative patients be avoided?
Transfuse blood of same RhD group
Group o-neg (RhD negative) used as emergency blood when a patients blood group not known
What percentage of donors are O-neg?
6-7%
Are there other red cell antigens present?
There are dozens e.g. Rh group-C,c,E,e; Kell, Duffy, Kidd etc.
Do not routinely match for all of them
8% patients transfused will form an antibody to one or more antigens
Once antigen is formed corresponding antigen negative blood must be used
Who is blood collected from?
Volunteer
Unpaid
17-70 year olds
What would exclude someone from donating?
Diseases that would make giving blood hazardous for them e.g. Cardiovascular or Neurological
If blood would be hazardous for recipient e.g. risks of viral, bacterial or parasitic infections.
What are the tests undertaken on donating blood?
Group and Screening
Infection test
What is the most important step in maintaining a safe blood supply?
Self-exclusion of individuals at high risk of transmitting blood-borne agents.
Since no test can pick up all infections especially early ones
What is prion disease?
A disease caused by prion proteins of variant Creutzfeldt-Jacob disease.
4 cases where donors who were entirely well donated bt developed the disease years later.
No test yet
How much blood is collected from a donor?
450ml
Why is is not effective to use ‘whole blood’?
Most patients need only one of the component of blood
Allows for more efficient use of donations and less waste
What is 1 unit?
Whole blood or blood products derived from one single blood donation
What are the main features of red cells?
Cells packages in SAGM nutrients, fluid plasma remover
Shelf life 5 week
Stored at 4 degrees
Given through a blood giving set that has a filter to remove clumps/debris
Rarely need frozen cells
What are the main features of fresh frozen plasma?
Stored at -30 degrees frozen within 6h of donation
Shelf lefe 3years
Must thaw 20-30 mins before use
Give ASAP within an hour or coagulation factors degenerate
Dose 12-15ml/kg
Need to know blood group
What are the main features of cryoprecipitate?
From frozen plasma thawed at 4-8 degrees overnight, residue remains
Contains fibrinogen and factor VIII
Storage and shelf life same as FFP
Standard dose from 10 donors
What are the two forms of Platelet concentrates?
Pooled platelets- from 4 donation pooled to constitute a single adult dose
From a single donor on a cell separator machine- equivalent to 4 single donations
What are the main features of platelet concentrates?
Stored at 22 degress
Constantly agitated
Shelf life 7 days
Need to know blood group
What are the main features of blood products by fractionation of plasma?
Large pool of plasma from 1000s of donors fractionated
What can be gained from fractionation of plasma?
Factor VIII and IX
-For haemophilia A and B
Immunoglobulins
- intramuscular, specific, fractionated from plasm from selected donor who have a high titre of specific antibody
- intramuscular, normal, broad mix in population e.g. to protect against hep A
- intravenous, can be used in some autoimmune disorders
Albumin
- 4.5% useful in burns, plasma exchanges
- 20% for certain severe liver and kidney conditions
