Blood Group Ags and Abs Flashcards
Describe the blood group antigens
36 known blood group systems
ABO and D are clinically most important
Ags in transfused blood can stimulate Ab response but only if the patient lacks the antigen
Likelihood of antibody formation increases as more transfusions are given
Antibody reactions in the body can be in vivo or in vitro. Describe these
In vivo (in body): leads to cell destruction either: directly when the cell breaks up in the bloodstream (intravascular)
Indirectly when liver and spleen remove Ab coated cells (extravascular)
In vitro (in the lab): reactions are normally seen as agglutination tests
What is agglutination? What can it identify?
When RBCs clump into visible agglutinates by Ag-Ab reactions
Results from Ab cross-linking with the antigens
As the Ag-Ab reaction is specific, agglutination can identify:
–presence of a red cell antigen (blood grouping)
–presence of an Ab in the plasma (Ab screening)
Describe the clinical significance of the ABO grouping system
- Ie what is common, and what can activate complement
A and B Ags v common (55% UK)
Anti-A, anti-B or anti-A,B Abs v common (97% UK)
ABO antibodies can activate complement causing INTRAVASCULAR HAEMOLYSIS
Draw a table to explain the ABO groups
Describe the clinical significance of the blood group ANTIBODIES
ABO Abs are usually produced in absence of antigenic stimulation
Some Abs=more clinically significant i.e. do more harm when encounter antigen in vivo
ABO, D, Kell, Duffy and Kidd are most clinically significant.
* MNS are sometimes clinically significant
* P1, Lutheran and Lewis are less so.
Describe the process of blood grouping
Test patient’s red cells w anti-A, anti-B and anti-D
– agglutination shows that a particular Ag is on the red cells, no agglutination= Ag is absent
Test patient’s plasma with A cells and B cells
– agglutination shows a particular antibody in the plasma or serum
– no agglutination shows the antibody is absent
Draw a diagram to show ABO compatibility
What is the Rh typing system? Specifically include the genetics of RhD and the main Ags
50+ antigens. Most important antigen is called D.
People w D Ag are D positive (85% of UK)
The other 4 main Rh antigens are known as C, c, E and e
D typing is most important after ABO, and patient is classified as D+ or D neg
Rh antibodies are clinically significant in transfusion and pregnancy, explain why this is
Transfusion: D Ag is very immunogenic, anti-D is easily stimulated -must PREVENT!
All Rh antibodies are capable of causing severe transfusion reaction- must have Ab DETECTION!
Pregnancy: Rh Abs=usually IgG and can cause haemolytic disease of the newborn.
Anti-D is still most common cause of severe HDN
Explain Haemolytic disease of the newborn and how we test for it
Blood group and Ab screen at 28 weeks to identify HDN risk
Atypical Abs are quantified periodically to assess su potential effect on the fetus
What is RAADP? (routine antenatal anti-D prophylaxis)
When is Anti D also given?
Anti-D injection binds to & removes any fetal D+ rbcs
Generally, 1500 iu of anti-D routinely given at 28 weeks and a smaller dose after delivery if baby D+
Anti-D also given after any event that may cause feto-maternal haemorrhage (bleed between mum and fetus), eg:
– Abdominal trauma
– Intrauterine death
– Spontaneous or therapeutic abortion
Describe the process of Ab screening
Patients serum mixed w 3 selected screening cells, incubated for 15min at 37, then centrifuged for 5min.
Clinically significant Abs at body temp identified using panel of known phenotyped red cells.
Specific antigen neg blood then provided for these patients to avoid an immune response.
What is the Zeta potential?
positive charges of the red blood cell makes it difficult for IgG to bind to the cell, so extra tests are needed in order for agglutination to occur
What is IAT?
Indirect anti-globulin test (IAT)
Used to detect IgG
LISS counteracts Zeta potential, results in agglutination. Used for:
– Ab screening and identifying
– Cross-matching donor blood w recipient plasma when hay known Abs or a previous history of Abs.
Cross-matching donor blood with recipient plasma is important when there are known antibodies or a previous history of antibodies.
Compare and contrast the different cross matching methods
