I am in the process of validating DATs on the TANGO and had some issues today with the negative DATs; the cell button on some were huge and the analyzer was interpreting them as ?.  I spoke with technical support and they indicated to mix the samples and centrifuge at a lower speed so the cells are not so packed.  It helped, but did not alleviate the problem.  Anyone have any suggestions?  Thanks!

Yes, we also have the "large button" problem on DATs and weak D tests.  We use a Stat Spin centrifuge, so most of our samples have a pretty packed button due to the higher RPMs.  Most of the time you are still able to read/interpret the reaction with the large button as you are able to see a significant amount of negative reaction around the button.  In this case we change the ? to negative and have the techs comment that the reaction was negative after visual inspection.

 

In the case where you can't clearly tell that it is negative, or the results are questionable in any way, we take a wooden stick and just loosen up the button on the bottom of the tube a bit and re-run the sample.  It usually works well.