Ever seen mixed field D typing (not transfused)?

[Mabel Adams]

Has anyone ever seen a mixed field (both Ortho MTS gel and tube using Quotient/Alba Anti-D blend at IS) D type in someone not recently transfused?  A recent prenatal sample showed this result but medium resolution molecular testing showed normal Rh genetics.  Ultrasound reportedly was fine with one baby. The molecular lab says we should still consider the patient Rh negative because she is not Type 1, 2 or 3 Weak D but she has an unusual serologic type.  We could order the high resolution testing for RHD-cDNA for another $750. I would like to hear of others' experience with something like this to better understand what the additional testing might tell us.  Apparently it won't tell us if she is a chimera  but would identify any mutations in the RHD gene.  but would we then know if she could make anti-D?

[Malcolm Needs ☆]

Actually, the D mosaic phenotype, where some red cells appear to be D Positive and some D Negative, is more common than many people think.  This has nothing to do with the individual having a genotypic mutation, per se, but is more to do with the mutation of a particular clone of red cell production within the bone marrow; it does not necessarily mean that there is any underlying clinically significant pathological condition.

The problem is that it is almost impossible to demonstrate a D mosaic without going through the whole rigmarole of testing that you describe.  However, there are anti-D kits available that will show, to all intents and purposes (with the exception of Partial D Type III - which is an exulted D type anyway, despite being a Partial D type) that there is a mosaic there (mixed-field reactions with all reagent anti-D sera), rather than a Weak or Partial D (usually a clear positive or negative reaction with the individual reagents).  Such kits are not cheap in themselves, but I doubt if they are as expensive as $750.

[Mabel Adams]

Are you referring to the Alba Partial D kit?

[Mabel Adams]

Also, do you have any references to help me make sure I understand the mosaic mechanism vs. chimera?  If I follow you, chimeras would have a mixed red cell population from the embryo stage but a mosaic might have had a spontaneous mutation in a red cell precursor line at a later time. Is that right?  Is this similar to how it works for people whose D antigens weaken with leukemia?

 

 

[Malcolm Needs ☆]

Hi Mabel,

Yes, I was referring to the Alba Partial D kit.

In addition, yes, you are quite correct in what you say about the difference between a "true" chimera and the spontaneous mutation and your comments about leukaemia.

The best I have read on this is in Daniels G.  Human Blood Groups.  3rd edition, 2013, Wiley-Blackwell.