blood transfusion Flashcards
ABO system
chromosome 9
A+B genes code for transferases which modify precursors called H substance on red cell membrane
A+B are dominant (co-dominant) over O
O is silent
phenotype vs genotype
phenotype = which antigens are detected
genotype = which genes are present
example
phenotype = Group A
genotype = AA or AO
group AB = AB
Landsteiners law
when an individual lacks A or B antigen the corresponding antibody is prodcued in their plasma
naturally occurring antibiodies cause haemolysis of red cells expressing the specfic antigen
ABO group A, where/what antigens/antibodies are presented?
antigens present on RED CELLS = A
antibodies present in the PLASMA = anti-B
ABO group O, where/what antigens/antibodies are presented?
antigens present on RED CELLS = none
antibody present in the plasma = anti-A AND anti-b
ABO group B, where/what antigens/antibodies are presented?
antigens present on RED CELLS = B
antibody present in the plasma = anti-A
ABO group AB, where/what antigens/antibodies are presented?
antigens present on RED CELLS = A AND B
antibody present in the plasma = neither
reagent to detect antibody/antigen specificity in pre-transfusion testing
reagent with known antibody specificity to identify antigen present on red cell -> antisera
red cells with known antigen specificity to identify antibodies present in plasma - > reagent red cells
how are patients blood groups defined
- Test patient’s red cells with anti-A, anti-B and anti-D antisera
a. Identify antigens on the red cells
b. IgM reagents – direct agglutination - Test patient’s plasma against reagent red cells of group A and group B
a. Identify antibodies in the plasma
which reagents would show positive agglutination in blood group A positive?
patient RED CELLS + anti-A
pateint RED CELLS + anti-D
patient PLASMA + group B cells
which reagents would show positive agglutination in blood group O positive?
patient RED CELLS + anti-D
patient PLASMA + group A cells
patient PLASMA + group B cells
indirect antiglobulin test
reagent red cells expressing know antigens
- add patient plasma
- add anti-human globulin
look for agglutination
indirect coombs test
detect antibodies in SERUM
method
- add patients PLASMA to RBCs with known antigen
- add Coombs reagent
- compare similarities in positive samples
uses
- pre-transfusion-testing - blood types, crossmatching
- pre-natal antibody screen - IgG antibodies that can cross the placenta
*CANNOT detect complement (complement on surface)
indications for red cell transfusion
- SYMPTOMATIC anaemia - Hb <70 - <80 if cardiac disease
- major bleeding
always consider alternative
transfuse a single unit of red cells then reassess
dications for platelet trnsfusion
- prophylaxis in patients with bone marrow failure + very low platelet counts
- treatment of bleeding thrombocytopenic patient
- prophylaxis prior to surgery/procedure in thrombocytopenic patient
always consider cause before transfusion
