Overview of Cell Viability and Cell Viability Assays

The viability of a cell or population of cells is an overall measure of the health of the cells. Viability assays are designed to assess the physical and metabolic state of the cell in order to determine the impact of treatment or culture conditions on cellular homeostasis.

The critical link between cellular health and disease underscores the necessity for assays that can measure cell viability in different experimental contexts and model systems.

How to Measure Cell Viability

Cell viability is measured using a variety of techniques and experimental platforms. Some techniques, such as enzyme-linked immunosorbent assay (ELISA) based viability assays, utilize spectral-based microplate readers for analysis. Other commonly used assays employ immunofluorescence, flow cytometry, or western blotting as a readout.

Cell viability vs cell proliferation assays:

• Cell viability assays - measure indicators of cell health, such as plasma membrane permeability, cellular metabolic activity, and levels of ATP.
• Cell proliferation assays - measure the quantity of viable cells through analysis of DNA content, DNA synthesis, or the expression of proteins required for cell division.

Cell Viability Assays

Multiple techniques are used for measuring cell viability. To confirm experimental outcomes, multiple independent assays should be performed. Techniques for analyzing cell viability include:

Assay	What is Measured
XTT assays Resazurin assays	Measure mitochondrial activity in viable cells	XTT Cell Viability Kit #9095: C2C12 cells were seeded at varying density in a 96-well plate and incubated overnight. The XTT assay solution was added to the plate and cells were incubated. The absorbance at 450 nm was measured at 1.0, 2.0, 3.0, 4.0, and 5.0 hours.
7-AAD/CFSE Cell-Mediated Cytotoxicity Assay Kit Propidium iodide Ghost Dye™ 7-AAD	Cell viability dyes are used to monitor dye uptake into nonviable cells; the dyes are excluded from entering viable cells	Ghost Dye™ Red 780 Viability Dye #18452: Flow cytometric analysis of live and fixed/permeabilized human peripheral blood mononuclear cells, combined and stained with Ghost Dye™ Red 780 Viability Dye. Viable gate is indicated.
Phospho-histone H3 (western blot) Proliferating cell nuclear antigen (PCNA) Ki-67 (IHC)	Measure expression levels of proteins required for (or involved in) cell division.	Ki-67 (D2H10) Rabbit mAb (IHC Specific) #9027: Immunohistochemical analysis of paraffin-embedded human colon carcinoma using Ki-67 (D2H10) Rabbit mAb (IHC Specific).

Assay	What is Measured
XTT assays Resazurin assays	Detect metabolic activity from viable cells with active mitochondria
XTT Cell Viability Kit #9095: C2C12 cells were seeded at varying density in a 96-well plate and incubated overnight. The XTT assay solution was added to the plate and cells were incubated. The absorbance at 450 nm was measured at 1.0, 2.0, 3.0, 4.0, and 5.0 hours.
7-AAD/CFSE Cell-Mediated Cytotoxicity Assay Kit Propidium iodide Ghost Dye™ Trypan blue	Cell viability dyes are used to monitor dye uptake into nonviable cells; the dyes are excluded from entering viable cells
Ghost Dye™ Red 780 Viability Dye #18452: Flow cytometric analysis of live and fixed/permeabilized human peripheral blood mononuclear cells, combined and stained with Ghost Dye™ Red 780 Viability Dye. Viable gate is indicated.
Phospho-histone H3 (western blot) Proliferating cell nuclear antigen (PCNA) Ki-67 (IHC)	Measure expression levels of proteins required for (or involved in) cell division.
Ki-67 (D2H10) Rabbit mAb (IHC Specific) #9027: Immunohistochemical analysis of paraffin-embedded human colon carcinoma using Ki-67 (D2H10) Rabbit mAb (IHC Specific).