Gel & Tube Rh Discrepancy

[Ward_X]

We have a male SSP historically A POS with a transfusion rxn to an AB POS platelet. The current sample was tested in gel, with cards that are DVI-. The pt also had a previous TRXN also to a plt that was Rh POS.

The rxn displayed a weakly positive post-DAT, with the followup pre-DAT significantly more positive. The resultant ABORh in tube on both the post and the pre samples are A NEG rather than Rh POS. Our bench reagent is a human-derived monoclonal Anti-D.

My question is, how can we have such a huge discrepancy between gel and tube for testing for D? Is this an anti-D, or is there a biochemical answer for the reactivity seen with the mechanism of bead agglutination in the column?

 

[Mabel Adams]

Ortho gel is known for picking up weaker D antigens than some tube reagents.  I know that Quotient/Alba anti-D blend reacts more like the Ortho gel but the Immucor Gammaclone doesn't pick up those (mostly) weak D types 1 & 2 at IS.  They will show up positive at AHG phase with Immucor.  John Judd published a paper, which many follow, of considering anything 2+ or weaker in gel as Rh negative. I assume if you take the tube testing through AHG you will get a positive.  Doing that will help troubleshoot the situation. None of this probably has much to do with the transfusion reactions.  Rh typing of weak and atypical D antigens is a complicated mess both serologically and the terminology. If these are young females, we try to send them for molecular D typing.