Why does post-thaw viability matter more than pre-freeze viability?

Cryopreservation and thaw are the steps most likely to damage cell membranes. A viability figure taken before freezing does not describe what is actually administered to a patient after cryopreservation and shipment, so post-thaw viability is the figure with clinical relevance.

Does a Certificate of Analysis prove viability?

Only if the COA explicitly states a viability percentage, the method used, and the specific lot it applies to. A sterility result or an infectious disease screen does not establish viability, and a generic product spec sheet is not the same as a lot-specific result.

Who tests stem cell viability?

Viability testing should be performed by a laboratory independent of the manufacturer, so the result is not self-reported, with the method and result documented on a lot-specific Certificate of Analysis.

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Regenerative Medicine · Provider Reference

What Is Stem Cell Viability?

Q: What is stem cell viability?

Stem cell viability is the percentage of cells in a given sample that are alive and intact at the moment of testing, typically measured with a dye-exclusion assay such as trypan blue or acridine orange/propidium iodide on a flow cytometer or automated cell counter.

The number that determines whether a vial contains living cells capable of engraftment — and the one figure most stem cell marketing quietly skips.

Reviewed by ATOM's Medical Team · Last updated September 2026

The Scientific Answer

Stem cell viability is the percentage of cells in a sample that are alive and structurally intact at the moment they're tested. It's a membrane-integrity measurement, not a count of total cells present. A vial can contain millions of cells and still have poor viability if a large share of those cells are dead or dying.

Viability is almost always measured one of two ways:

Trypan blue exclusion — a dye that only penetrates cells with compromised membranes. Live cells exclude the stain and appear clear under a hemocytometer or automated counter; dead cells take up the dye and appear blue.
Flow cytometry with a viability dye (e.g., 7-AAD, propidium iodide, or acridine orange/PI on instruments like the Nexcelom Cellometer) — higher resolution, and typically preferred for regulatory-grade release testing because it can be paired with identity and phenotype markers in the same run.

The result is expressed as a simple ratio: live cells ÷ total cells counted, reported as a percentage. A lab reporting 90% viability means 9 in 10 cells counted excluded the dye and were classified as live at the time of the assay.

Viability is not the same as cell count, identity, or potency. A product can be 95% viable and still fail an identity panel if the cells aren't the type claimed. These are separate tests answering separate questions, and a complete Certificate of Analysis reports all of them independently.

Why Post-Thaw Viability Is the Number That Matters

Cryopreservation and thaw are the two steps in the entire supply chain most likely to damage a cell. Ice crystal formation, osmotic stress during the freeze/thaw transition, and the cryoprotectant itself all put mechanical and chemical stress on the cell membrane — which is exactly what a viability assay is measuring.

That means a viability figure taken before a product is frozen tells a provider almost nothing about what will actually be in the syringe. The only figure with clinical relevance is viability measured after the product has gone through the same freeze, storage, and thaw cycle the patient's dose will go through.

What can lower post-thaw viability

Freeze rate — uncontrolled or non-rate-controlled freezing increases intracellular ice formation
Cryoprotectant formulation and concentration
Storage temperature stability during transport (temperature excursions in the cold chain)
Thaw technique and time-to-administration after thaw
Cell type — some populations tolerate cryopreservation better than others

This is also why a viability percentage should always be read as lot-specific, not as a fixed product specification. Two lots processed under an identical protocol can still return different post-thaw results, which is why the figure belongs on a per-lot Certificate of Analysis rather than a marketing page.

What to ask any supplier: "What is the post-thaw viable cell count for this specific lot, and what method was used to measure it?" A sterility panel, an infectious disease screen, and a generic spec sheet all answer different questions — none of them answer this one.

How ATOM Documents It

Post-Thaw Viability, Per Lot

ATOM cell products are released against a post-thaw viability standard, measured on the actual lot after cryopreservation and thaw — not projected from a pre-freeze sample. Testing is performed by an independent third-party laboratory, so the result isn't self-reported.

Every unit ships with a lot-specific Certificate of Analysis that states the viability result, the method used, and the lot number stamped on the physical vial — so the number on the document matches the product in the provider's hand, not a generic average across the catalog.

If you want to see what that documentation actually looks like before you order anything:

View a Sample COA

References

Dominici M, et al. Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy. 2006. View source →

This page is educational reference material for licensed healthcare providers and does not constitute medical, legal, or regulatory advice. HCT/P products are not FDA-approved. Testing methods and results referenced for ATOM products are documented per lot on that lot's Certificate of Analysis.