How is cell viability percentage calculated?

Viability percentage = viable cells ÷ total cells counted × 100. With dye exclusion, unstained cells count as viable and stained cells as dead. This can be done manually on a hemocytometer or with an automated counter using trypan blue or AO/PI. The viable cell count, as an absolute number or concentration, is usually reported alongside the percentage, because a high percentage can still mean too few cells [2][3].

Trypan blue vs MTT: which cell viability assay should I use?

Trypan blue classifies individual cells by membrane integrity and gives a viable count and percentage. That suits cell suspensions and product release. MTT and other tetrazolium assays measure average metabolic activity per well over 1–4 hours. That suits plate-based proliferation or cytotoxicity screening [1]. Trypan blue can overestimate viability compared with AO/PI and struggles with debris [2]. Metabolic assays can be skewed by reducing or fluorescent compounds [1].

Why does cell viability drop after thawing cryopreserved cells?

Freezing and thawing damage cells, and part of the cell death is delayed. In a 2020 study of bone marrow mesenchymal stromal cells, viability fell most at 2–4 hours after thawing and recovered to 93.1–97.6% by 24 hours. Metabolic activity and adhesion were still impaired at that point [8]. Viability measured right after thawing can therefore miss later cell loss and does not show function.

Does higher cell viability mean better fat graft survival?

Not necessarily. Adipocyte or SVF viability is a laboratory measure taken before grafting, and results depend strongly on the assay. For example, trypan blue can count dead adipocytes as live [7]. Studies use viability to compare harvesting and processing methods; one study reported median adipocyte viability of 73–85% depending on the liposuction technique [7]. Graft retention in the patient is a separate clinical outcome that depends on many other factors.

Cell Viability

别名: 세포 생존율

发布 2026年9月14日更新 2026年9月20日

What is an acceptable cell viability for cell therapy products?

For cell therapy products, the FDA generally expects a minimum viability specification above 70%, and sponsors must justify a lower limit with data [2]. NK-cell trials in the US and Europe used ≥70% across the board [4]. Some products use stricter limits. The commercial specification for the CAR T product tisagenlecleucel is at least 80%, although a 2019 analysis found no link between viability below 80% and remission rates [3].

已验证 2026年9月18日

关键事实

属性	值	来源
Definition of a viable cell	A cell with an intact membrane or the capacity for metabolism, motility, proliferation or response to stimuli截至 2022年1月19日	[1]
Dye-exclusion principle	Trypan blue enters cells with damaged membranes and stains them blue; unstained cells are counted as viable截至 2022年1月19日	[1]
Common plate-reader assay classes	Tetrazolium reduction (MTT, MTS, XTT, WST-1), resazurin reduction, protease substrate (GF-AFC), ATP luciferase and real-time luminescent assays截至 2016年7月1日	[2]
Typical research uses	Measuring cell proliferation, testing compounds for cytotoxic effects, and as an internal control for viable cell number in multiplexed assays截至 2016年7月1日	[2]
ATP assay characteristics	Described as the fastest and most sensitive viability assay and less prone to artifacts, but it is an endpoint assay that lyses cells截至 2016年7月1日	[2]
Trypan blue measurement variability	Image-based trypan blue scoring depends on microscope optics, cameras and settings; heat-killed cells took up about 50% more dye than formaldehyde-fixed cells in a NIST study截至 2022年1月19日	[1]
Related standard	ISO 20391 (Biotechnology — Cell counting), cited in NIST work on traceable viability measurement截至 2022年1月19日	[1]
CAR T (CTL019) viability release specification	At least 80% for the commercial product; early clinical trials used at least 70% %截至 2019年1月1日	[3]
Viability and clinical outcome (CAR T)	No link was found between product viability below 80% and response, expansion or survival in 123 pediatric ALL and 25 adult DLBCL patients截至 2019年1月1日	[3]
NK cell therapy viability acceptance range	≥70% in all reviewed Phase 1/2 trials; assay protocols were not harmonized across trials %截至 2025年11月11日	[4]

概述

Cell viability is the number or proportion of living cells in a sample. It is usually reported as percent viable cells or as viable cells per unit volume. Because 'viable' is defined by what a test measures (an intact membrane, or functions such as metabolism or proliferation), results depend on the assay used. Dye-exclusion methods, such as trypan blue or fluorescent dyes read by automated counters, check whether the cell membrane is intact. Plate-based assays measure tetrazolium or resazurin reduction, protease activity or ATP. Viability is used in cytotoxicity testing, cell culture, cryopreservation research and as a release criterion for cell therapy products, where clinical trials have commonly used thresholds of 70–80%. ISO 20391 covers cell counting methods. Readers should check which assay, instrument and definition a reported figure is based on.

What is an acceptable cell viability for cell therapy products?

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