---
title: "Cell Viability"
url: "https://worldwiki.io/entity/cell-viability"
type: "concept"
language: "en"
updated: "2026-11-12 05:20:00"
independence_score: "100.00"
independent_mentions: "0"
authority_mentions: "0"
---

# Cell Viability

Cell viability is the proportion of living, functional cells in a sample; it is a key quality measure for cell preparations such as SVF before and after processing or freezing.

## Key facts

- **Definition of a viable cell**: A cell with an intact membrane or the capacity for metabolism, motility, proliferation or response to stimuli [1]
- **Dye-exclusion principle**: Trypan blue enters cells with damaged membranes and stains them blue; unstained cells are counted as viable [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 [2]
- **Typical research uses**: Measuring cell proliferation, testing compounds for cytotoxic effects, and as an internal control for viable cell number in multiplexed assays [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 [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 [1]
- **Related standard**: ISO 20391 (Biotechnology — Cell counting), cited in NIST work on traceable viability measurement [1]
- **CAR T (CTL019) viability release specification**: At least 80% for the commercial product; early clinical trials used at least 70% [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 [3]
- **NK cell therapy viability acceptance range**: ≥70% in all reviewed Phase 1/2 trials; assay protocols were not harmonized across trials [4]

## Overview

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.

## Related entities

- related to → [Stem Cell Fat Grafting](https://worldwiki.io/entity/stem-cell-fat-grafting)
- related to → [Stromal Vascular Fraction](https://worldwiki.io/entity/stromal-vascular-fraction)
- related to → [Cryopreservation](https://worldwiki.io/entity/cryopreservation)

## Related questions

- [How is cell viability percentage calculated?](https://worldwiki.io/q/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 
- [What is an acceptable cell viability for cell therapy products?](https://worldwiki.io/q/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% a
- [Trypan blue vs MTT: which cell viability assay should I use?](https://worldwiki.io/q/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
- [Why does cell viability drop after thawing cryopreserved cells?](https://worldwiki.io/q/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
- [Does higher cell viability mean better fat graft survival?](https://worldwiki.io/q/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]. Stu

## References

Independent 4/4

1. [Quantitative, traceable determination of cell viability using absorbance microscopy](https://pmc.ncbi.nlm.nih.gov/articles/PMC8769294/) — PLoS One · evidence level B · independent · evidence page: https://worldwiki.io/source/251
2. [Cell Viability Assays (Assay Guidance Manual)](https://www.ncbi.nlm.nih.gov/books/NBK144065/) — National Center for Biotechnology Information (NCBI Bookshelf), Riss TL et al. · evidence level B · independent · evidence page: https://worldwiki.io/source/134
3. [CAR T cell viability release testing and clinical outcomes: is there a lower limit?](https://pmc.ncbi.nlm.nih.gov/articles/PMC6872962/) — Blood (Chong EA et al.), 134(21):1873–1875 · evidence level B · independent · evidence page: https://worldwiki.io/source/136
4. [Quality standards for NK cell immunotherapies](https://pmc.ncbi.nlm.nih.gov/articles/PMC12644036/) — Frontiers in Bioengineering and Biotechnology (von Werz et al.) · evidence level B · independent · evidence page: https://worldwiki.io/source/137