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Forum Name: Obstetrics

Question: am i sensitized to o pos blood?


 kbqld - Thu Jan 29, 2009 6:04 am

I am wanting to fall pregnant with my fourth child. My third child's blood type is O + and mine is O neg. I had a klihauer when she was born and it came back negative, so i decided not to have any anti d. I have had a blood test which has come back with a positive antibody screen from a GROUP AB SCREEN, but insufficient specimen for titre. The DIRECT COOMBS test is negative, and my EXTENDED BLOOD GROUP is C- c+ E+ e- K-. My gp is unsure how to read these results and has referred me to a specialist. From what i have read on the net i think i may NOT have been sensitized to Opos blood (based on direct coombs result) What can you tell me? thankyou
 Dr. Chan Lowe - Sat Jan 31, 2009 11:47 pm

User avatar Hello Kbqld,

The 4 blood types, A B AB and O, are basically delineated by two antigens or "markers" on the red cells. There are A antigens and B antigens. Those with blood type O do not have either of these antigens, those with AB have both. The + or - part of the blood type refers to another antigen referred to as the D antigen.

The Coombs test looks for antibodies that bind to red blood cells. These antibodies can bind at a number of different sites, not just the D antigen site, so a negative coombs test does not necessarily mean that you are not sensitized to the + factor. This test would look for antibodies to your red cells but the issue with these sensitizations is that the body forms antibodies to the baby's red cells so the coombs test is not helpful for determining these reactions.

Given that both you and your baby are blood type O, there would not be expected to develop any antibodies against A or B antigens (since your baby's blood does not have these antigens). This leaves the +/- interaction (along with any possible "minor" antigen reactions that are uncommon but can be significant). The Rhogam injection is an anti-d antigen antibody. The way it works is that the mother is injected with the anti-D antibody. Then, if any of baby's blood gets into mother's bloodstream and the baby is D + (has the D antigen on it's blood cells), the D antibody binds to it and "covers it up" so that the mother's body never really is able to see it. This prevents the mother's body from recognizing the D antigen and making antibodies against it on its own. The Rhogam antibodies then go away after time and the mother no longer has any D antibodies in her blood so the next baby is safe from attack by them.

To determine if you have been sensitized to the D antigen, you need to be tested for anti-D antibodies. If they are not present, you have not been sensitized to the D antigen.

The extended blood groupings you list are other antigens (some of the "minor" antigens). For this information to be more helpful for you, you would need to know what your children's extended groupings were. Basically, any time that a mother is negative and a child is positive for an antigen, there is a risk of sensitization. These antigens are much less common to develop a sensitization to than is the D antigen.

The Kleihauer-betke test (also known as the Kleihauer test) is a test used to look for fetal blood in the mother's blood stream. Theoretically, if the test were negative, none of the baby's blood entered the mother's bloodstream to start off the sensitization process. One must be cautious of this, though, since this test is not 100% sensitive.

This issue can be a bit confusing to explain and understand so I hope I have made some sense to you. To sum up all this, from the information you have given it is not possible to say whether or not you have been sensitized. Further testing would be needed if you were concerned.

Best wishes.

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