What are the limitations of cell viability assays?

Most cell viability assays can only give information at the population level. These assays do not give spatial information about viability variations in a cell population, which is important for understanding cell-to-cell interactions. Cell viability assays provide quantitative data only. They may not be able to distinguish between different forms of cell death or provide insight on the mechanisms. Sensitivity may also be an issue in detecting low levels of cellular death. Some cell viability assays may only provide information at a specific time point. For example, cell survival may be influenced by the length of treatment or cell death markers may only be present at specific stages of the cell death process.