What are the limitations of colorimetric assays of cell viability and cytotoxicity?

Although colorimetric assays are easy to perform and relatively economical, they have a few limitations. The exact limitation depends on the dye being used for that specific assay. Limitations of colorimetric assays of cell viability and cytotoxicity may include: 

• MTT is highly toxic to cells.
• MTT is insoluble in water, necessitating an additional formazan dissolution step.
• MTT may interfere with cell culture medium, compromising the results.
• Crystal violet staining assay is insensitive to changes in cell metabolic activity.
• The measurements in LDH assay may be affected by serum or other compounds that have inherent LDH activity. 
• The measurements in XTT assays may be affected by cellular ion concentration, enzymatic regulation, cell cycle variation, pH, or other environmental factors.
• The measurements in SRB assay may be affected by cellular aggregates or clumps. 
• The measurements in MTS assays may be affected by cell type, incubation time, and cell count.
• The measurements in WST-8 assay may be affected by changes in intracellular metabolic activity that has no direct impact on cell viability.