TUNEL microscopy quantification - (Oct/11/2012 )

I'm doing TUNEL assay on adherent cells and attempting to quantify via confocal fluorescent (FITC) microscopy. My positive control (DNase) give a good strong signal, filling most of the nucleus. However, most of my samples produce a much, much weaker signal. My question is, how much FITC signal do I need to see to call a cell TUNEL-positive? Should the signal extend throughout the nucleus? Would appreciate any comments. Thank you.

Most people do TUNEL to quantify DNA damage. Why are you doing this test exactly? I hope you know that FITC does not stand for confocal microscopy because you sound otherwise. Also, FITC is not a really strong dye, it is kinda old fashioned and needs expertise to get strong signal. It is difficult to tell how much you need to call it a positive result, you must run controls and compare.