LDH activity has a long history as a preferred marker for cell death with in vitro cell models [43, 44] . In HTS applications, the activity of LDH is indirectly measured by an enzymatically-coupled reagent chemistry comprised of lactate, NAD + , diaphorase and an appropriate redox dye such as a tetrazolium compound or resazurin. Although the result of LDH activity can be measured by a change in absorbance, fluorescence detection is favored because of greater sensitivity and the potential to miniaturize to high-density plates.