Does the strength of a reaction correlate with the severity of a fetomaternal hemorrhage?

[Mosaics]

So the other day, I had an interesting question from a neonatologist.  Her question (and I am summarizing, not directly quoting) was in regards to a microscopically positive DAT and if there is less antibody present.  Her concern was how aggressively she needed to treat the baby, because the baby was jaundiced at less than 12 hours.

 

Mom was O pos, baby A pos, and had microscopically positive DAT.  So there was some ABO incompatibility

 

I wasn't completely sure how to explain this, but my co-worker said there was a smaller fetal bleed.

 

Today, I was reading a text that stated "the strength of the reaction does not correlate well with the severity of the HDN."  The text was Modern Blood Banking & Transfusion Practices, 5th edition, by Denise Harmening, page 389.

 

So in your experience, does the strength of a reaction correlate with the severity of a fetomaternal hemorrhage?  How should I explain this in the future?  Thanks y'all.

 

 

[Malcolm Needs ☆]

I would agree that there is no correlation between the strength of the DAT and the severity of the HDFN (ABO HDFN quite often has a negative DAT), but I would thoroughly disagree with the comment that a weak DAT means that there was a smaller foetal bleed.  There is very little correlation between the amount of the foetal bleed and the strength of the maternal antibody.  There is much more correlation between the immunogenisity of the foetal antigen and the strength of the maternal antibody.

[galvania]

It's a bit scary that the neonatologist thinks the strength of the DAT is the criterion she needs to know as to how aggressively to treat the baby!  I would have thought that the baby's symptoms would have indicated that!  the positive DAT is a guide as to WHY the baby might be haemolysing; in some cases it might be a guide as to how strong the haemolysis is - A 4+ (i. e. max) result with anti-IgG on a baby whose mum has an anti-D titre of 1000 is unlikely to leave the baby unaffected - but I hope the ante-natal team would have reacted before then!  But haven't we all seen 2+ DATs with no effects at all and +/- ones where the baby is quite ill?