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we were told that agglutination occurs when the matching antibody react with its antigen on the RBC surface (as antibody B with antigen B).... Also when blood transfusion, Donors plasma with antibodies is diluted , so when o-donor gives blood to B-recipient , B antibodies ( of the donor) is diluted
........ My question is in lab cross-matching test when we put recipient's plasma(o with b antibodies for example) on the donor's RBCs (B with b antigens)..... is there agglutination, If so, how would we know the right group then?....if not ,Why not? if the whole thing is misunderstood ,i wish to be told how it's done.

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Disregarding Rh factor for a moment: when you add A-antibodies to a blood sample and agglutination occurs, this means the blood contained A-antigens (A-type). The same can be said for a sample of blood to which B-antibodies are added (B-type). If agglutination for both antibodies occurs in separate assays on the same sample of blood, it means the sample contains both A and B antigens (AB-type). If the sample is said to be O-type, this means neither A or B antigen would be present in these cells. It's safe to transfuse O-type blood into any recipient due to this fact. What you also want to watch out for, is attack on the recipients RBC's by antibodies in the donor's plasma. This can result in a hemolytic transfusion reaction (HTR), but it's noted in the following text:

Red blood cell incompatibility may also occur when the patient's RBC antigens are attacked by antibodies from the donor's plasma. This tends to be a minor problem because of the small amount of antibody present in the donated plasma, which is further diluted on transfusion into the recipient's circulation.

If you're in the lab doing a Coombs test, for example, you're checking to see if there are any extraneous antigens present that might results in a HTR. In a normal result, ergo there aren't any antibodies to RBC's in the sample mixture, you wont see any agglutination. This is for considerations outside of ABO antibodies, generally. If you're adding to B-type RBC's a plasma with known antibodies to B antigen, like O-type plasma, you can probably expect an event. To my knowledge, O-type plasma wouldn't be safe to give to anyone but an O-type recipient.

additional source

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  • $\begingroup$ what i know is that o is the universal donor what i don't get is how do we know it's compatible when its plasma has the antibodies or is it not done this way at all(mixing donor's RBCs and recipient's plasma)? $\endgroup$ – Magdy Shehata Jul 24 '15 at 5:37
  • $\begingroup$ O group RBC's lack antigens to either A or B antibodies, making them suitable for donation to any blood type. The recipients body wont attack the donor RBC's. The donor plasma contains antibodies to both A and B antigens, however. The assumption we're making is that out of total blood volume, donor + recipient, the amount of A/B antibody in the O group plasma will be dilute enough that there's a deleterious effect on hemolytic events involving donor anitbodies. What you wouldn't do, is give O group plasma to anyone other than an O group recipient during a plasma transfusion. $\endgroup$ – CKM Jul 24 '15 at 15:42
  • $\begingroup$ The way we find out if it's compatible, is we add A and B antibodies to separate samples of blood to determine if agglutination occurs. For O group blood, you wont see any of this. To confirm, you can back type the blood. Take the O group serum, and add either A blood cells or B blood cells to separate samples. You should see clumping in both cases (you're type AB if no clumping occurs in back typing). $\endgroup$ – CKM Jul 24 '15 at 15:49
  • $\begingroup$ is cross matching done with the blood of the donor and recipient or not ? $\endgroup$ – Magdy Shehata Jul 25 '15 at 7:54
  • $\begingroup$ It's done with the serum of the recipient, and the donor's packed red blood cells. $\endgroup$ – CKM Jul 25 '15 at 13:14

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