Blood transfusion Flashcards
Humans have antibodies against antigens not present on their red blood cells - what class of antibodies?
IgM class
reactive at 37 degrees
Capable of fully activating complement
Can cause fatal haemolysis
A patient with AB blood will have what antigens on their red blood cells and what antibodies in their plasma?
A and B antigens
No antibodies
A patient with O blood will have what antigens in their red blood cell and what antibodies in their plasma?
No antigens
Anti A and Anti B antibodies
How are A and B antigens on red blood cells structured and formed?
By adding one or other sugar residue onto a common glycoprotein and fucose stem ( also known as the H antigen )
A antigen will have a galnac sugar extra
B will have a Gal sugar extra
What is the structure of Group O antigen?
Has neither A or B sugar, has only the H stem
Ceramide - glu - gal - gnac - gal - fuc -
What do the genes do to encode for specific red blood cell antigens?
e.g.
A gene codes for an ENZYME that then adds the sugar ( N-acety galactosamine ) to the common H antigen
B gene codes for an enzyme that adds galactose
- A and B are co dominant
- O is recessive
What is the affect of antibodies responding to foreign red blood cell antigens?
Agglutination can be seen ( lab tests )
- Group O can be given to anyone in emergency if their own blood group is unknown
What does it mean to be RhD positive?
Have a D antigen ( and vice versa )
Their genes are D = codes for D antigen on cell membrane ( DD, Dd )
d = no antigen and is recessive
Can people who lack the RhD make anti-D antibodies?
Those who are RhD negative can make antibodies once exposed
- Either by transfusion of RhD positive
- Women pregnant with a RhD positive feotus
- once sensitized, need to avoid in the future
What class are Anti-D antibodies?
IgG class
What would be the implications if a RhD negative px pre-exposed to D-antigen had a transfusion from a RhD positive px?
Delayed haemolytic transfusion reaction :
anaemia, high bilirubin, jaundice
What would be the implications if a RhD negative mother pre-exposed to D-antigen had a RhD positive feotus?
issue for their next pregnancy - if that foetus also has RhD positive
mother’s antibodies can cross placenta and attach to the baby’s blood cells = haemolysis
Hydrops fetalis and death
If baby survives - high bilirubin can cause brain damage or death post birth
What is Group O negative blood?
Group O blood, RhD negative
why may there be a delayed reaction post transfusion even if the blood type matches?
Other red cell antigens may be present on the red blood cell
- need to test for an antibody and then find corresponding blood - antibody screening
How does antibody screening take place?
Patient plasma incubated with 2-3 different screening specific red blood cells which have alot of antigens
If screen is negative - any suitable blood can be given
If positive antibody must be identified with a large panel of red blood cells to find suitable donor blood
