negative Cord DAT, positive eluate

[QCDan]

Increasingly we are seeing the following and we are wondering about the DAT IgG that we are using and the sensitivity. 

Mom has antibody, baby cord blood has a negative DAT, we perform an antigen typing on baby (if positive) we perform elution on the cord sample. frequently we are finding that we are able to elute the antibody that mom is positive for from the baby cord cells.

Question is this. We are seeing slightly elevated bilirubin on initial and 9 hour posts, along with elevated transcutaneal bilirubin.

anyone else seeing this? or does anyone have suggestions?

[Malcolm Needs ★]

One thing I would say is that the baby should be treated on clinical symptoms, rather than on laboratory results, particularly when they are so weak that you have to do all this testing to show an abnormality in the Blood Bank.

A slight rise in bilirubin is normal in a newborn baby.

This situation is very similar to the difference between a haemolytic transfusion reaction, where, for example, there is a positive DAT, antibody can be eluted and there is a SIGNIFICANT rise in bilirubin and a SIGNIFICANT drop in Hb, and a serological transfusion reaction, where there may, or may not be, be a positive DAT, antibody may or may not be eluted from the red cells, a new antibody specificity may be detected in the plasma, but there is NO SIGNIFICANT rise in bilirubin and NO SIGNIFICANT drop in Hb.  Your cases remind me strangely of the latter.

[srichar3]

It could be that the cells are coated but not sufficient to get a positive result. However when you perform the eluate on a large enough number of RBC'c the amount of IgG removed from these red cell's is then enough to coat and cause a positive reaction on the screening cells. Also the cells from the DAT will be heterozygous cells, hence you will get a stronger reaction from screening cells that are homozygous if sufficient antibody is eluted to coat them. 

[Jane12]

We usually perform an elution whenever Mom has an antibody & the newborn baby is positive for that antigen regardless of the DAT result. In 25% of cases the eluate is positive . It depends on concentration of Mom's antibody coating the baby's red cells. There could be prozone effect as well. 

[John C. Staley]

I have to ask, how many times when the DAT is negative and you can elute the antibody from the babies cells does the infant show symptoms of a significant case of HDN (old guy, old nomenclature) resulting in an exchange transfusion or even phototherapy?  Seems to me you are doing an awful lot of work for little, if any, benefit.  See Malcolm's technical discussion above.