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Pink EDTA Tubes Used in Antibody Screens


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On behalf of a CAP accredited lab, the following question was received: "We have been using pink top tubes for about 5 years in the blood bank.  We got to thinking that calcium is chelated in these tubes.  We were further thinking that calcium is needed for complement activation.  So, we wonder if when we do antibody screens, panels and crossmatches whether we will never see hemolysis even when an antibody is present which would have caused hemolysis when we used clot tubes.  Does anyone know??

 

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Actually, Ca++, Mn++ and Mg++ ions are all chelated by EDTA, and all of them are required for complement activation through to haemolysis.

The antibodies that gave suspicion as to their specificity by haemolysis (apart, of course, from rip roaring ABO antibodies) were anti-H (from an Oh individual), anti-I (from an adult ii individual), anti-PPKP1 from a pp individual and an anti-Vel.  As no Ca++, Mn++ or Mg++ are present, you will not see haemolysis with these antibodies in any of the tests you mention, however, you will, except in very rare cases, see agglutination.  In some 43 years in, usually, Reference Laboratories (so we saw most specificities), I know of only one case were an anti-Vel was missed in the UK because the anti-Vel was so weak by IAT using EDTA plasma, but was quite strong using serum, and Jill Storry has also described such a case (although I do not have her citation to hand).

I really wouldn't worry about it.  It is just SOOOOOOOOO rare.  It is a bit like a patient with an anti-Wra being given Wr(a+) blood by electronic issue, after a clear antibody screen.  It happens, but you wouldn't abandon electronic issue on such a rare happening.

Edited by Malcolm Needs
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No, and you won't Scott (or, at least, you shouldn't!), because changes in storage affect the serum that allow non-specific uptake of proteins on to the red cells, causing false positive DAT results - something that does not happen (never say never!) with EDTA plasma.

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