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srichar3

Weak D test

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Back in the days when we used to do blood groups in micro-titre plates manually, we always did the Du test as we called it then to pick up the weak D's. Since moving to gel technology in the beginning we picked up loads of D pos's that had previously been classed as neg due to the higher sensitivity of the Card methods. Since than I have worked at a few different labs and some have dropped the weak D tests and other have maintained them on newborns. I find the test a bit of a pain as the only time I find it positive now is when there is a positive DAT, I don't ever remember 1 occasion where the card D test was negative but the IAT D test was genuinely positive. 

Has anyone else who still does this test actually found a positive when the card Rh-d was negative? 

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13 hours ago, David Saikin said:

you really need to do the test on O Neg cord bloods unless your gel Anti-D detects the DVI.  Of course, if you do donors, it is required to call a unit Rh Neg.

We have extra Sera for DVI as Ortho dont do a DVI+ cassette, so at the minute were are doing both Weak-D and DVI on the RH-D neg cords.  

I'm pretty sure the Weak-D also doesn't detect DVI.

Edited by srichar3
update

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Just checked the info and seems it does detect DVI, a bit sneaky of the rep to include this as extra when its not needed with the weak-D sera.

"The blend of antibodies in this blood grouping reagent will directly agglutinate D positive red cells and may directly agglutinate red blood cells from most weak D and partial RhD including DVI. In addition the reagent will detect most partial D, and most weak D by IAT and, therefore, is suitable for RhD grouping of donor samples."

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I agree with you srichar3, from the patient side, and with you David Saikin, from the donor side.

I also cannot remember the last time that I either came across a D phenotype that was so weak that we only detected it by IAT, certainly since the introduction of really good monoclonal anti-D blends.  We certainly, as a Reference Laboratory, had cord bloods sent to us to confirm the expression of Partial DVI, but this always worried me, for three reasons.  Firstly, the evidence that Partial DVI is sufficiently immunogenic to actually sensitise a mother to produce anything but a very weak allo-anti-D is, to say the least, flimsy.  Secondly, I cannot ever remember a hospital sending us in a sample from the mother, to check whether she, herself, was also Partial DVI, meaning that she would not require anti-D immunoglobulin, because the baby's Partial DVI would have come from genes that she had passed on to the baby.  Thirdly, as anti-D immunoglobulin is derived from human polyclonal anti-D (monoclonal anti-D immunoglobulin has yet to be shown to be efficacious) and, therefore, is a possible vector of transfusion-associated disease, such as novel viruses, as yet unknown.  If these women do not definitely require anti-D immunoglobulin, it is a moot point as to whether it should be offered to them without very good grounds.

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Malcolm - I have a patient at my small hospital here: O POS w anti-D.  Sent her specimen to Ms Moulds at Gamma (circa 1992).  Mom came back as DVI.  Besides anti-D she also has Jka.

Nice letter from MM but still needed to provide some input to the OB guys.

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With monoclonal reagents I have seen maybe 3 or 4 cord bloods that surprised me with a positive result for the weak D test. One of those, mom and baby were IS negative and weak D positive very weakly. We don't send those patients out for molecular testing at this time.

We also don't do weak D testing on adults unless a fetal bleed screen is strongly positive, the sample is from the Rh negative male partner of an OB with anti-D, or it's part of a preliminary workup for an potential organ/stemcell donor. We routinely perform weak D testing on cord bloods and newborns.

 

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1 hour ago, David Saikin said:

Malcolm - I have a patient at my small hospital here: O POS w anti-D.  Sent her specimen to Ms Moulds at Gamma (circa 1992).  Mom came back as DVI.  Besides anti-D she also has Jka.

Nice letter from MM but still needed to provide some input to the OB guys.

Oh yes David.  I did not mean that individuals who are Partial DVI cannot make anti-D; far from it - they often do when stimulated.

What I meant was that the evidence that these individuals can stimulate anti-D in a true D Negative individual is pretty sketchy.

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