[When is Rhesus D positive in test tubes?]

Sorry, in response to your question, the mother had a clear meg reaction on the cards so we didn’t test her further. The cord blood tested 0.5, rerun was neg and the second rerun was a query which is why we went for a tube group.

[When is Rhesus D positive in test tubes?]

Thank you so much for your input. Our concern was merely regarding the mother being avoidably sensitised by us missing a weak reaction. Our tubes and anti sera are at room temp (replaced daily) so I don’t think it’s a reaction to the cold but that is a good point for future reference. 

[When is Rhesus D positive in test tubes?]

While this seems a fairly obvious answer, we’ve had issues lately. Two weeks ago, we had a cord sample give a ‘?’Reaction in Rh D in the newborn card. As per our sop, this was rerun and came up negative and to be sure, the bms washed the cells and checked the group in test tubes.  It was weakly positive in one clone of Rh D, only detectable under the microscope. This was later confirmed as weak D by the reference lab and the mother was dosed appropriately with Anti-D. 

Historically, we’ve always checked negative test tube  Rh D under the microscope and this rarely caused problems. Since this incident though, we’ve had problems with weak (+/-) reactions which are confirmed as negative by the reference lab. Anti sera instructions state observation is macroscopic which would overrule our historic habit of checking microscopically BUT how else do you detect weak Rh D? If we had followed the macroscopic only rule, we would have missed the weak Rh-D and the mother could have been sensitised. Is weak Rh D in a foetus less likely  to cause sensitisation?