Whitney Poplin

Yeah ..... I obviously didn't think that one through. Probably hadn't had enough caffeine yet.

Thanks Whitney for posting this question!  I do not have an answer, but your question is an opportunity for me to learn. 
 
I was wondering how low prevalence antigens from the MN CHO collection would cause steric hindrance.  After reviewing information in The Antigen Fact Book, I am reminded that the MNS antigens are on GPA and GPB which are single-pass membrane sialoglycoproteins.   One of the major functions of sialoglycoproteins is to contribute to the negative charge of the RBC glycocalyx.
 
The antigens in the MN CHO blood Group Collection, which are more frequently found in Blacks, are also on GPA and GPA and have altered sialic acid. 
 
So, if cell #6 of this Ortho panel has one of these low incidence antigens, there is a stronger negative charge and this stronger charge is weakening the anti-M/M antigen reaction?  Is that correct?  Wow--that would never have occurred to me.
 
I hope you get an answer!  A call to Ortho seems to be in order!
 
And, I hope I do not change the course of this thread too much when I ask if others have seen cases where steric hindrance has caused negative reactions when a positive reaction would be reasonable.
 
Catherine Baldwin CLS, MT(ASCP)SBBcm

In my experience the DAT is highly subjective to variables such as the method/reagent, the laboratory technique of the technologist (e.g. 'shaking' of the tube), reaction grading, and the circumstances surrounding the test performance (e.g. what else is going on to delay the testing/disorient the technologist).
This is basically why we permit microscopic readings. I'd rather that someone saw the 1+ reaction that they shook away as a microscopic reaction due to poor/hasty technique. It's also not a help that the manufacturer insert clearly indicates: "examine negative reactions with an optical aid."

Hi Karrieb61,
Are you referencing performing eluates for pos-transfusion investigation or for mother/baby ABO incompatibility?
My view is that the DAT is a crappy test . . . er, ahem . . . it is not a sensitive test.  One can easily get a negative DAT and end up getting a specificity out of the eluate, since the eluate concentrates the antibody. 
At our facility we currently look at all DAT's microscopically, which is a bit of carryover from previous management.  We do eluates on micro + DAT's if the patient has been transfused in the last 2 weeks.  If I remember right, we have gotten specificities out of eluates performed on samples with micro + DAT's (at least if I remember right.  Help me out here, Mabel.) For babies, we still report the DAT as pos (even if just micro+) and that is where the workup stops.  We don't do further investigation to prove it is maternal anti-A or anti-B causing the positive DAT.  However I suppose we would investigate further if the physician requests us to do so.

Yeah ..... I obviously didn't think that one through. Probably hadn't had enough caffeine yet.

Current screen is negative so e- AHG crossmatch compatible unit.
 
If screen was positive today I would give C-,K-,e-  AHG crossmatch compatible units.