A caspase is a type of protease that when activated cleaves protein substrates. This leads to the cell becoming disassembled, showing signs of the beginning stages of apoptosis, or programmed cell death. Therefore, this makes caspases an ideal biomarker to use to detect apoptosis. The most common caspase assays come in kits and use fluorometric, colorimetric, or flow cytometry-based methods. These assays are typically used with other cell death assays to gain a complete picture.