Though simple visual techniques of observing viability can be useful, it can be difficult to thoroughly measure an organism's/part of an organism's viability merely using the observation of physical properties. However, there are a variety of common protocols utilized for further observation of viability using assays. • Tetrazolium reduction: One useful way to locate and measure viability is to complete a Tetrazolium Reduction Assay. The tetrazolium aspect of this assay, which utilizes both positive and negative charges in its formula, promotes the distinction of cell viability in a specimen. • Resazurin reduction: Resazurin Reduction Assays perform very closely to that of a tetrazolium assay, except they use the power of redox to fuel their ability to represent cell viability. using
7-Aminoactinomycin D (7-AAD), wherein a lower signal indicates viable cells. Therefore, this case shows good viability (viability of the cells in flow cytometry should be around 95% but not less than 90%.). • Cytolysis or membrane leakage: This category includes the
lactate dehydrogenase assay. Assays such as these contain a stable enzyme common in all cells that can be readily detected when cell membranes are no longer intact. Examples of this type of assay include
propidium iodide,
trypan blue, and
7-Aminoactinomycin D (7-AAD). • Mitochondrial activity or caspase:
Resazurin and
Formazan (
MTT/XTT) can assay for various stages in the
apoptosis process that foreshadows cell death. • Functional: Assays of cell function will be highly specific to the types of cells being assayed. For example,
motility is a widely used assay of sperm cell function.
Gamete survival can generally be used to assay
fertility.
Red blood cells have been assayed in terms of
deformability,
osmotic fragility,
hemolysis,
ATP level, and
hemoglobin content. For
transplantable whole organs, the ultimate assay is the ability to sustain life after transplantation, an assay which is not helpful in preventing transplantation of non-functional organs. • Genomic and proteomic: Cells can be assayed for activation of stress pathways using
DNA microarrays and protein chips. • Flow Cytometry: Automation allows for analysis of thousands of cells per second. As with many kinds of viability assays, quantitative measures of physiological function do not indicate whether damage repair and recovery is possible. An assay of the ability of a
cell line to adhere and divide may be more indicative of incipient damage than membrane integrity.
Frogging and tadpoling "Frogging" is a type of viability assay method that utilizes an agar plate for its environment and consists of plating serial dilutions by pinning them after they have been diluted in liquid. Some of its limitations include that it does not account for total viability and it is not particularly sensitive to low-viability assays; however, it is known for its quick pace. "Tadpoling", which is a method practiced after the development of "frogging", is similar to the "frogging" method, but its test cells are diluted in liquid and then kept in liquid through the examination process. The "tadpoling" method can be used to measure culture viability accurately, which is what depicts its main separation from "frogging". ==List of viability assay methods==