Measuring cell viability is fundamental to reliable cell culture work.

Cell health and survival directly determine the quality and interpretability of almost every downstream experiment – from basic proliferation studies to high‑content screening, drug testing and omics analyses. If viability is poor or fluctuates between experiments, changes in readouts may reflect stressed or dying cells rather than true biological effects.

Routine viability assessment acts as an internal quality control for your cell cultures. There is an enormous variety of dyes, kits and methods on the market for determining cell viability. Below we list some excellent options from our portfolio.

1. Dye‑exclusion and live/dead staining

Membrane‑impermeant dyes enter only dead cells having compromised membrane integrity, while live cells exclude the dye. With dual‑color kits, one dye labels live cells and another dead cells. These kits are versatile and typically require a cell counter, microscope or a flow cytometer.

Examples from BioNordika’s suppliers:

• Trypan Blue from Logos Biosystems
• Erythrosin B from Logos Biosystems
• Acridine Orange-Propidium Iodide Kit from Logos Biosystems
• Live‑or‑Dye Fixable Viability Stains: multiple colors for flow and microscopy from Biotium
• ViaFluor SE Cell Proliferation Kits from Biotium
• Calcein AM Cell Viability Assay Kit from Biotium
• Viability/Cytotoxicity Assay Kit for Animal Live & Dead Cells from Biotium
• Calcein AM, Calcein Red, Blue and UltraBlue AM from Cayman Chemicals
• Ghost Dye Fixable Viability Dyes from Cell Signaling Technology
• Live Cell (LC) and Live Cell Multiplex (LCM) Assay from Indigo Biosciences

2. Metabolic tetrazolium assays (colorimetric)

Metabolically active cells reduce tetrazolium salts (MTT, MTS, XTT, WST‑1, WST‑8, etc.) to colored formazan products, measured by absorbance. MTT assay requires cell lysis before the absorbance can be measured. XTT and resazurin do not require cell lysis, allowing measurements to be made at multiple timepoints.

Examples from BioNordika’s suppliers:

• MTT Cell Proliferation Assay Kit from Cayman Chemicals
• MTT Cell Viability Assay Kit from Biotium
• XTT Cell Proliferation Assay Kit from Cayman Chemicals
• XTT Cell Viability Assay Kit from Biotium
• WST‑1 Cell Proliferation Assay Kit from Cayman Chemicals
• WST-8 Cell Proliferation Assay Kit from Cayman Chemicals

3. Resazurin / Alamar Blue‑type assays (fluorescent or colorimetric)

Resazurin is a non‑fluorescent, blue dye that easily enters cells. In metabolically active (viable) cells, mitochondrial and cytosolic reductases convert resazurin into resorufin, which is pink. Increase in fluorescence is proportional to metabolic activity thus to the number of viable cells. Because the assay is usually non‑destructive and one‑step, resazurin kits are very convenient for routine viability, proliferation and cytotoxicity testing in 96‑ or 384‑well plates.

Examples from BioNordika’s suppliers:

• Resazurin Cell Viability Kit from Cell Signaling Technology 
• Resazurin Cell Viability Assay Kit from Cayman Chemicals
• Resazurin Cell Viability Assay Kit from Biotium

4. ATP‑based luminescence assays

All living cells contain ATP, whereas ATP levels drop rapidly when cells die. In these assays, cells are lysed and their ATP is used as a substrate in a luciferase–luciferin reaction, producing light. The luminescent signal is directly proportional to the amount of ATP, and thus to the number of viable cells, whereas dead or severely damaged cells contribute little or no signal.

Because of their high sensitivity, wide dynamic range and simple workflow, ATP‑based luminescence assays are ideal for high‑throughput viability, proliferation and cytotoxicity screening.

Examples from BioNordika’s suppliers:

• ViaLight® Plus Cell Proliferation and Cytotoxicity BioAssay Kit
• Steady-ATP™ HTS Viability Assay Kit from Biotium

5. Membrane‑integrity / enzyme‑release assays

LDH-based assays measure cell death via the release of intracellular enzymes.

Lactate dehydrogenase (LDH) is normally retained inside cells. When the plasma membrane is damaged (necrosis or late-stage apoptosis), LDH leaks into the culture medium. In LDH assays, this enzyme activity in the supernatant is detected by a coupled enzymatic reaction that produces a colorimetric or fluorescent signal.

The signal is proportional to the amount of LDH released, and thus to the degree of cell damage or cytotoxicity.Because LDH is measured in the medium, the assay is non-destructive for the remaining cells and is ideal as a complementary “cell death readout” to metabolic viability assays (e.g. WST‑1 or resazurin).

Other enzyme‑release assays, such as ToxiLight, follow the same principle with different markers. For example, ToxiLight measures the release of adenylate kinase (AK) instead of LDH, using a luminescent readout. When cell membranes are compromised, AK is released into the medium, where it drives a bioluminescent ATP‑generating reaction.

The luminescence correlates with membrane damage and cytotoxicity. ToxiLight kit provides a highly sensitive, non-destructive cytotoxicity assay, permitting use of cells for additional analyses or repeated sampling.

Examples from BioNordika’s suppliers:

• ToxiLight™ bioassay kit  from Lonza
•  LDH Cytotoxicity Assay Kit from Cayman Chemicals

6. Flow cytometry‑based viability and apoptosis assays

Flow cytometry–based viability kits combine single‑cell resolution with multiparameter analysis. They use fluorescent dyes and/or conjugated proteins to distinguish live, apoptotic and dead cells based on membrane integrity, externalised phosphatidylserine or DNA accessibility. Typical formats include:

Fixable viability dyes (amine‑reactive “live/dead” dyes) that label membrane‑compromised cells more strongly than live cells and are compatible with fixation and multicolour panels.

Annexin V–based apoptosis kits, often combined with DNA dyes like PI or 7‑AAD, to separate live, early apoptotic and late apoptotic/necrotic populations.

Dual‑ or multi‑color live/dead kits that integrate seamlessly into existing flow panels, adding a robust viability gate without sacrificing key markers.

These assays are ideal when you need quantitative, multiparameter viability data at single‑cell level, for example in immunophenotyping, drug response profiling or apoptosis studies.

Examples from BioNordika’s suppliers:

• Ghost Dye Fixable Viability Dyes from Cell Signaling Technology
• Live‑or‑Dye Fixable Viability Staining Kits from Biotium
• CF Dye Annexin V conjugates, NucSpot and RedDot nuclear dead‑cell stains from Biotium for combined apoptosis/viability analysis

Download the Cell Viability and Cell Death brochure from Biotium.