Until recently, the only methods available to measure cytotoxicity were qualitative ones. These methods are subjective and rely on the skill of a microbiologist to identify malformed or lysed cells. Based on what the operator sees in the microscope, a determination of whether or not a material is cytotoxic is made.
The most recent revision of ISO 10993 (Biological Evaluation of Medical Devices), describes quantitative methods for cytotoxicity testing. ISO 10993-5:2009 states that while qualitative cytotoxicity methods are useful for screening purposes, quantitative cytotoxicity methods are now preferred for determining material cytotoxicity.
Annex C of ISO 10993-5 refers to the MTT assay as a prescribed quantitative cytotoxicity method. The MTT has several benefits over traditional qualitative cytotoxicity methods. It can accurately measure as few as 950 cells, it can be performed on material extracts or through direct contact, and the results are not subjective, increasing repeatability. Additionally, the MTT is a colorimetric assay and as such a standard microplate reader can be used to analyze the results, increasing throughput ability.
Pacific BioLabs has recently introduced the MTT Assay for cytotoxicity as an available test method, and the results have been very positive. The sensitivity of the assay, coupled with objective readings, provide study sponsors with greater information and increased confidence in the results. Therefore, we recommend quantitative assays such as the MTT for all final cytotoxicity data purposes.