Blood Transfusions Flashcards
what is activating complement
are able to cause potentially fatal haemolysis (destruction of red cells) if incompatible blood is transfused.
Blood group A (rbc type,antibodies in plasma and antigens in rbc)
rbc = a
antibodies in plasma= anti b
antigens in rbc= a antigen
Blood group B
rbc type= b
antibodies in plasma= anti a
antigens in rbc= b antigen
Blood group AB
rbc type= ab
antibodies in plasma= none
antigens in rbc= a and b antigens
Blood Group O
rbc type= o
antibodies in plasma= anti a and anti b
antigens in rbc= none
how are a and b antigens formed of red cells
by adding one or other sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane.
Group O has neither A or B sugars – H stem only
What does the A gene do
Codes for an enzyme that adds N-acetyl galactosamine to the common H antigen
What does the B gene do
Codes for the enzyme which adds galactose
Are A and B genes co dominant
Yes
Is O recessive or dominant
Recessive
What are the possible genes for blood group A
AA or OA
Possible genes for blood group B
BB or OB
Why is it safe to give blood group O to anyone in an emergency
As group O has no ABO antigens
RhD negative
dd
RhD positive
DD or Dd ( is d gene codes for no antigen and is recessive)
Can people who lack the RhD antigen make anti D antibodies
Yes, after they are exposed to the RhD antigen, either by transfusion of RhD positive blood or in women if they are pregnant with an RhD positive foetus. Anti-D antibodies are IgG class antibodies
Implications of anti D antibodies on future transfusions
1) future transfusions; patient must in future have RhD negative blood (otherwise their anti-D would react with RhD positive blood - causesdelayed haemolytic transfusion reaction– with anaemia; high bilirubin (from breakdown of red cells); jaundice etc.).
Implications of anti-D antibodies on HDN
haemolytic disease of the newborn-if RhD neg mother has anti-D, then in the next pregnancy, if fetus is RhD positive: mother’s IgG anti-D antibodies can cross the placenta (only IgG class antibodies can do this) – attach to the RhD positive red cells of the foetus and cause haemolysis of foetal red cells - if severe:hydrops fetalisand death. If less severe, the baby survives but after birth, the high bilirubin levels can cause brain damage or death.
How to avoid sensitisation of RhD negative patients
- Transfuse blood of same RhD group
- Group O negative blood
Steps needed to provide ABO and Rh compatible b
Pod
Test ABO and RhD blood groups of patients red cells and an antibody screen on the patients plasma ( group and screen),
How is an antibody screen performed
- Patient plasma is incubated with 2 or 3 different fully typed’screening’ red cells, which are known to possess all the blood group antigens which matter clinically.
* If the antibody screen is negative, any donor blood which is ABO & RhD compatible can be given.
* If the antibody screen is positive, the antibody must be identified with the use of a large panel of red cells. Donor units of blood that lack the corresponding blood group antigen are then chosen for cross matching with the recipient’s plasma prior to transfusion.
Compatibility testing before transfusing patients
. Patient blood sample (plasma + cells).
• ABO group (test patient’s red cells with known anti-A and anti-B reagents).
• RhD group (test patient’s red cells with known anti-D and reagent).
• Select donor blood of the same ABO & RhD group.
• Antibody screen +/- antibody panel, to identify antibody/ies.
2.Cross-match:patient’s serum mixed with chosen donor red cells - should not react: if reacts (agglutinates) = incompatible.
Blood with X antigens will agglutinate with an anti-X reagent.
Why may blood donors be excluded
if they have any disease that might make blood donation hazardous for them, e.g. cardiovascular/ neurological disease, or if their blood would be hazardous for the recipient (risk of viral, bacterial or parasitic infections, certain diseases or drugs).
Donor education and self-exclusion of individuals who are at high risk of having contracted blood-borne infectious diseases are essential to ensure that individuals who are in an early infectious stage, in whom the infection is not yet detectable by any test (i.e. in the’window period’of infection) do not donate.
Infection testing done on all blood samples
HIV, hep B , hep C , hep E , HTLV and Syphillis
Infection testing done on some samples
CMV, T.cruzil, Malaria. Blood test to exclude vCJD is not yet available
How is blood separated
450 ml of blood is collected from donor into a sterile plastic bad containing an anti-coagulants and centrifuged. Not efficient to use whole blood as patients only need one component. Eg. When giving anemic patients red cell transfusion, they don’t need the excess fluid contained in the plasma part as this puts them at risk of fluid overload.
So whole blood is centrifuged into three parts:
Red cells bottom
Platelets middle
Plasma top
( then squeeze each layer into satellite bags and cut free)
What could red cells given be used to treat
Anaemia without volume deficiency
What could platelets given be used to treat
Platelet deficiency
What could FFP given be used to treat
Any coagulation factor decline
What could cyroprecipitate given be used to treat
Factor 8, VWF , 13 deficiency, fibrinogen , fibronectin ( made from FFP)
