All tags Cellular and biochemical assays Cytotoxicity assay guide

Cell health

Cytotoxicity assay guide

Learn about your options when you need a cytotoxicity assay.

A cytotoxicity assay is often based on assessing damage to cellular membranes.

Cytoxicity assay methods

See below to learn more about these assay methods, or review our most popular cytotoxicity assay kits including the LDH assay, DRAQ7®, and our combined dye live:dead cell assay.

Alternative methods of performing a cytotoxicity assay, measure it indirectly, by measuring cell viability, ie the number of healthy cells in a population. Learn about how to run a cell viability assay, such as by using MTT, MTS, resazurin, mitochondrial membrane potential-dependent dyes, cellular esterase cleaved dyes, or by measuring the levels of ATP, ADP, glycolytic flux or oxygen consumption.

You can also learn about apoptosis assays, such as Annexin V, TUNEL and caspase assays, and about cell proliferation/cell cycle assays, such as assays using dye dilution, BrdU/EdU and DNA staining dyes.

The Sulforhodamine B assay is a further alternative cytotoxicity assay method using the level of binding of the Sulforhodamine B dye as a proxy for the number of live cells.

Enzyme leakage

These assays measure the activity of enzymes that leak into the extracellular medium on cell membrane damage. The most popular assay is for lactate dehydrogenase.




Assay kits

LDH/Lactate dehydrogenase

Plate reader

LDH oxidizes lactate and a colored, or fluorescent (Ex/Em 535/587 nm) product is formed.


AK/Adenylate kinase

AK converts ADP to ATP with detection via luciferase light-generation.
AK activity is not as enduring as LDH.


Membrane impermeable dyes

Cell viability assays often use membrane-impermeable fluorescent dyes (mostly DNA stains) that stain cells with damaged cell membranes. Propidium iodide has largely been replaced by DRAQ7™ and 7-AAD for cell viability assays due to its broad emission spectra and tendency to bind to live cells.




Assay kits


Flow cytometer, microscope

Ex/Em 633 & 647/665–800 nm. DNA stain.



Ex/Em 488/647 nm. DNA stain.

Propidium Iodide

Ex/Em 536/617 nm. DNA stain.Leaches from cells over time.


Ethidium homodimer-1

Ex/Em 528/617. DNA stain.

Trypan blue


Non-fluorescent cell stain. Classic cell viability assay that requires cell counting. Best for small sample numbers.

Amine-reactive dyes for live:dead cell assays

Amine-reactive dyes weakly stain viable cells by binding to cell surface amines and strongly stain membrane-compromised cells by reacting with intracellular amines. Dead and live cells can be differentiated by fluorescence level.




Assay kits

Amine-reactive dyes

Flow cytometer

Ex/Em 410/450 nm.
Fixation compatible (applies to all dyes in this table).

Ex/Em 408/512 nm

Ex/Em 398/550 nm

Ex/Em 353/442 nm

Ex/Em 498/521 nm

Ex/Em 547/573 nm

Ex/Em 583/603 nm

Ex/Em 649/660 nm









Combined dye live:dead cell assays

Multiple dyes can be combined in a single live:dead cell assay. Examples include the popular live and dead cell assay (ab115347) with ethidium homodimer to label dead cells and an esterase-cleaved dye for live cells. The alternative, cell viability assay kit (fluorometric – dual green/red) (ab112121), includes a red DNA staining dye for dead cells and a green esterase-cleaved dye for live cells.

Learn more with our:

Cell viability assay guide
Measure the rate of continuing cellular activities, such as metabolism.

Cell proliferation and cell cycle assay guide
Monitor the growth of a cell population using cell staining dyes, detect generations of daughter cells, or analyze the cell cycle state of a cell population.

Apoptosis assay guide / cell death analysis guide
Measure the markers present in different types of cell death.

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