We have found some variation across our Transfusion Services departments who perform Weak D testing for Cord ABO/Rh testing ordered for Rhophylac work ups.  I am curious to know if testing commercially available Weak D cells is required for quality control for this test.  We all perform a DAT if the Weak D is showing a positive result and use check cells when the Weak D is showing negative results. Any feedback is appreciated, thanks!

I'm not aware of any quality control requirements for weak D testing.  Looking at two different manufacturer's inserts for anti-D, I did not see any requirements for quality control testing for weak D.  In addition, our daily quality control of the anti-D reagent does not involve testing a known weak D.  It will be interesting to see if anybody else knows of a requirement for weak D testing.

I've never used Weak D control cells.  What I'd really like is a DVI cell to verify that my tube D will detect it but not available.

I've always used IgG sensitized cells to QC my negative AHG reactions.

I would advise people to look at RH/index.htm.  There are now WELL over 100 (almost 200) different weak D types, not to mention the number of Partial D types.  Unless you have access to ALL of these red cells, AND use them as a control EVERY time you perform this test, you cannot QA/QC this test.  There are times, even in the world of blood transfusion/blood group serology, you just have to admit defeat and keep your fingers crossed!  Even if you were using molecular, rather than serological techniques, you would have to perform complete RHD sequencing each time to ensure you would detect all known mutations AND any novel mutations.

We have defined Weak D as IS negative with an IgM anti D and Positive in the IAT phase with an IgG Anti D (often a blend).  We have made weak D cells here that can work as a control in manual tests.  I have not included D variants in my work as these show different reaction patterns with the various commercially available anti D's.

2 hours ago, noelrbrown said:

We have defined Weak D as IS negative with an IgM anti D and Positive in the IAT phase with an IgG Anti D (often a blend).  We have made weak D cells here that can work as a control in manual tests.  I have not included D variants in my work as these show different reaction patterns with the various commercially available anti D's.

I am sorry noelrbrown, but I don't think your definition of a Weak D would pass muster.  There are now 170 different Weak D types that are officially recognised, and by no means would all of these react as you suggest.  I still maintain that it is virtually impossible to come up with a true positive and negative quality control, even leaving out both Partial D types AND those types that are not yet designated as either Weak or Partial (of which there are very many).  Any quality control that does not take this into account is no more than a sop (and by that, I don't mean a Standard Operating Procedure, but a mere gesture) to show that an effort has been made, but that gesture is actually doing nothing but salving a conscience.

Edited November 25, 20195 yr by Malcolm Needs
Clarification.

Malcolm, I agree with you and understand exactly what you are saying.  My challenge is more to do with interpreting requirements from reagent manufacturers and regulatory bodies.  Therefore that is why i said "we" it being the Royal "we".

I can't think of a single regulatory requirement that says the Anti-D reagent has to be tested against a Weak D positive Cell so this would be subject to local regulations and Medical Director preference. Immucor package insert for Anti-D Series 4 and corQC attached for reference.corQC; 381-6.pdfAnti-D (Series 4) 336-9.pdf

 

Personally, I like the idea expanding our QC of Anti-D reagent with a cell that is known to be non-reactive at the immediate spin phase and reactive at the IAT phase. But, this is just extra cost and is not required.

 

 

Deep Dive Question: Should we be thinking on a more fundamental level with this QC than what some have suggested?

There are two clones of Anti-D in most reagents used for bench testing: an IgM clone and an IgG clone. When testing controls at the immediate spin phase we are verifying the reactivity of the IgM clone. Taking cells through the weak D phase should provide adequate control for the reactivity of the IgG clone. IAT testing should be performed on both positive and negative cells.

Analogous Example:

With Polyspecific AHG reagent there are 2 different clones present: an anti-IgG clone and an anti-complement clone. QC is not accomplished through testing with IgG check cells and a negative control with unsensitized cells, a QC test must be performed for the anti-complement reactivity as well.

 

 

 

 

NWBloodBanker, this is not so in the UK (and probably in most, if not all, of Europe).

This site is multinational/worldwide, and while what you have written may be COMPLETELY TRUE for the USA, it is NOT true for the entire world.