Cell proliferation and viability assay kits are often used to investigate the metabolic activity of cells in culture after exposure to stimuli or toxic agents. Additionally, increases or decreases in cell growth can be a sign that a cell culture has been contaminated or undergone genetic drift.

ATCC offers two cell proliferation assays, MTT and XTT, that utilize the reduction of tetrazolium salts to enable the safe, accurate, and straightforward quantification of changes in cell metabolism or proliferation.

MTT cell proliferation assay kits have been optimized to expedite sample processing. The MTT reagent yields low background absorbance values in the absence of cells. For each cell type, the linear relationship between cell number and signal produced is established, thus allowing quantification of changes in the rate of cell proliferation.

The second generation tetrazolium dye, XTT, can be effectively used in cell proliferation, cytotoxicity, and apoptosis assays. XTT is reduced to a soluble, brightly colored orange derivative by a mix of cellular effectors. The sensitivity of an XTT assay is greatly improved by the usage of an intermediate electron carrier, PMS (N-methyl dibenzopyrazine methyl sulfate). PMS helps drive XTT reduction and formation of its formazan derivative.

The applications for these assays include drug sensitivity, cytotoxicity, response to growth factors, and cell activation. Both assays are highly sensitive, reproducible, and adaptable to high-throughput screening.