The mom is O Neg with an Anti-D due to RhIG. The baby is B pos with a 3+ DAT. The physician orders an elution. The Anti-D shows up in the eluate and the A1 and B cells are both 3+ with the eluate. Are the reverse cells both positive simply because of the ABO incompatibility and how is this proven?

Well you would definitely want to check first whether the A and B cells are D+

The other thing to do is check a sample of the anti-D (same batch) against A rr and B rr red cells, in case the anti-A and anti-B has been derived from the anti-D immunoglobulin.

Might in not also be a maternal anti-A,B?  In the US the reverse typing cells are Rh Neg (they must be that way in the UK, yes?).  I have seen both anti-D and an anti-A eluted from cord blood.

Yes David.  You are correct that it could be maternal anti-A,B.

 

Yes also David.  The reverse typing cells in the UK are rr - although this can, on rare occasions, be a bit of a pain when the patient has an anti-c that reacts at RT.

Agree with David and Malcolm about >A,B.   Run some more A1 and B cells (that are Rh neg) to rule in.   I am assuming you are getting negative reactions with group O Rh negative cells. 

Add me to the anti-A,B group.