What are the differences between MTT and WST assays?

MTT and WST assays are both colorimetric cell proliferation assays used to measure biocompatibility, which is a common pre-clinical evaluation for experimental procedure development. They are each named for the tetrazolium salt reagent that is their core component, which are reduced to their corresponding formazan dyes in living cells.

Figure 1. NADH reduction of MTT to Formazan in cytoplasm of viable cell.

MTT was the first used, developed in the 1980s along with the growing popularity of 96-well microplate assays. It is still widely used as the standard method to determine cell population and health, but since the MTT compound is cytotoxic and only remains stable for a few hours, other alternative assays have been developed. One of these is the WST assay, which has much lower cytotoxicity and is stable for up to 48 hours.

Although the assays are similar, they are suitable for different experimental designs, depending on the other preparation steps in the procedure, resources available, and sensitivity required.