MadSci Network: Immunology
Query:

Re: For use in transfusions, is blood typed 'further' than A, B, O, etc.?

Date: Tue Mar 20 16:36:43 2001
Posted By: Ann Gronowski, Faculty, Pathology, Washington University
Area of science: Immunology
ID: 984171518.Im
Message:

O positive is indeed the most common blood type.  The only testing that is 
routinely performed is for the major blood groups A, B, and O, as well as 
for Rh (positive or negative).  The reason we test for A, B, or O is 
because people have antibodies to the major antigens which their own red 
cells do not express (ie, people with type A have antibodies to type B 
antigens, etc.).  

However, there are hundreds of "minor" blood group antigens that are not 
routinely tested for because they do not generally cause a problem if a 
recipient of one type receives a transfusion of another type.  This is 
because people do not have preexisting antibodies to these minor 
antigens.  These minor antigens can cause a problem, however, in patients 
who get multiple transfusions.  For example, if a patient gets a unit of 
red cells that expresses minor antigen "x", and that patient's own red 
cells do not have antigen "x", then that patient may develop antibodies to 
antigen "x".  The next time that patient gets transfused with a unit of red 
cells expressing minor antigen "x", the antibodies may lyse those cells.  
These reactions to minor antigens are generally not life-threatening, but 
if the patient lyses the cells, it defeats the whole point of the 
transfusion.  

We don't screen for these antigens because 1) there are hundreds of them, 
and 2) they generally are not life threatening and 3) we would generally 
pick up a potential reaction during testing that is done prior to 
transfusion called a cross-match.  Cross matching is performed like this: 
Whenever a unit of red cells is being prepared for transfusion into a 
patient, we mix serum from the recipient with cells of the unit that we 
want to transfuse.  If there is a reaction, we can generally identify that 
the patient has developed one of these antibodies and can usually identify 
what that minor antigen is.  So if that patient needs blood, we now can 
screen donated units for the presence of antigen "x", and then pick ones 
which do not express antigen "x", thus avoiding a reaction.  These are 
especially important for antigens which are very common in the population.  
If a patient does not express antigen "x"  and has antibodies to antigen 
"x", but most of the population does express antigen "x", you can see why 
it might be hard to find compatible blood.  It may be the case that a unit 
of blood that you donated was screened in this way, and that perhaps you 
were found to lack an antigen which is commonly expressed in the general 
population.  This would make your blood important for people who have 
antibodies to antigen "x".

Giving blood is very important and a wonderful gift of life. Recently, I 
needed a blood transfusion so I thank you very much!!




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