We recently took part in an evaluation which involved doing antibody screens and ID panels with trial and routine cells using both automated and manual techniques. We have access to both Ortho and Diamed technologies so used both systems in our evaluation.

The samples used were all red cell antibody screen negative plasma samples which had been frozen and thawed. The samples were allowed to come to room temperature and spun before use. They were put though both analysers with no problems, however when we carried out the manual testing a large number of wells showed apparent dual population reactions. We then preheated the cells and plasma and repeated the tests. There were less dual population reactions but they did not disappear completely.

Has anyone else seen this and does anyone know of an explanation for this?

My guess is that this is residual fibrin. People and machines do not necessarily sample from the same place in the plasma tube. Try repeating the manual test taking plasma from the bottom, the middle and the top and see if there's a difference. Another tip is that if it is fibrin, you can fish it out from the top of the gel using a fine yellow Eppendorf tip (probably others too, but that's what I use) - but not the white Diamed tips - they aren't fine enough. I am presuming that these were all results that should have been negative. If they should have been positive, disregard what I say abaout fibrin