tompat wrote:
Dr. goljan says abo incompatibility protects against Rh incompatibility
 that is what I thought when I first saw this q hints.
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| tompat
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it's been given in goljan immuno path that abo incompatibility protects against developing Rh hemolytic disease.
he also mentions the same q at the end of the chapter.
so guys please tell again what u think about this one.
in any case D wont be the ans as we have 1.anti A or
2.if it has to develop anti Rh antibody .
so one of them will cause hemolysis during direct coombs.
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| drduck
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hey tompat even i read that......goljan has a different opinion than us....but he has a valid point.....
i give u example.....
what does the IgD immunisation does to the mother?????
it kills the sensitised RBCs...and prevent them from being read by memory cells...so,no further response........
now what goljan says?????
he says that in case of ABO incompatibility the mother already has antibodies against the respective antigen of fetus....might be A,B or both.....
now these preform antibodies also act against the RBC coated with D antigen......if anyhow they are formed...
so moment they come in contact the get killed by the same mechanism....
only difference is the the former was done actively and latter pasively.
tell me did it help u????
as this was my way of interpretation....
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| drduck
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according to me....the answer can be C or even D......
why not D....
let me explain,
she has concieved for the first time.....
only thing happened is leakage of fetal blood into maternal circulation
that means mother didnt have any preformed anti RhD in her blood.....
so no passage of any IgG into the fetus.....
so no antibody coated RBC in the fetus......
so NEGATIVE coombs test..........
plz tell me if am wrong
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| tompat
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hi drduck,
as u said above, the only diff is the former happened actively and later happened passively, let me tell u something,in this case jaundice is produced in the new born cause of ABO anti bodies.the fact that it occured in first pregnancy and it is not mentioned in q stem that there was any feto-meternal bleed.
now mother has anti A IgG aND IgM anti bodies as her blood group is O. here IgG is causing the cross placental hemolysis and IgM taking care of fetal RBCs coming in maternal blood. now IgM will destroy fetal blood cells with D antigen before they are processed and presented to memory cells . this is the only mechanism by which we can think that ABO incompatibility protects against Rh sensitization.
again coombs test is not exclusively for Rh ANtibody. it detects any antibody present against RBCs or whether rbcs have that antigen which a test sera can hemolys.
the fact that anti A IgG are present on fetal rbc's will make the direct coombs positive.
here when pt's RBCs are washed they will still have anti A IgG antibodies attached to them , after adding known antisera they will get hemolysed making the test positive.
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| drduck
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thankx........tompat,
good job....
i forgot about preformed antibodies of IgG class........yes coombs will be positive......
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