Population Doublings & Passages

Cultured cells have an age that has nothing to do with the donor's: how many times they have divided in the lab. Here is how that is measured, why the two common measures differ, and what to ask for.

Last updated October 7, 2026For licensed medical professionals4 peer-reviewed and regulatory sources

In short

A passage is one transfer of cells into a new vessel. A population doubling is one doubling of the cell number. Passage count is easy to report but varies with how full each vessel was; cumulative population doublings measure how much a cell population has actually divided. Published studies describe gradual changes as MSCs are expanded, so expansion history belongs on the lot paperwork.

Passage vs. population doubling

Two-panel diagram: population doubling shows one cell becoming 2, 4 and 8 cells with the formula PD equals log base 2 of cells harvested divided by cells seeded; passage shows one full flask detached and split into three new flasks.
Passage vs. population doubling. A passage counts transfers into new vessels. A doubling counts cell divisions. Illustration.
Passage (P) Population doubling (PD)
What it counts Each time cells are detached and re-seeded Each doubling of the total cell number
How it is calculated A simple tally (P1, P2, P3…) PD = log2(cells harvested ÷ cells seeded)
What it misses Two P3 lots can differ widely if vessels were split at different densities Requires accurate counts at every seed and harvest
Best use Process step tracking Comparing expansion history across lots and suppliers

Cumulative population doublings (CPD) add the doublings from every passage. If 1 million cells are seeded and 8 million harvested, that passage added 3 doublings (2 × 2 × 2 = 8). Spread across five passages, the same cells might reach 12 to 15 cumulative doublings while still being labeled "P5."

Five culture flasks labeled P1 to P5 adding 3, 3, 2.5, 2 and 1.5 doublings, with a running total rising to 12 cumulative population doublings and cells drawn progressively larger and flatter.
Cumulative doublings across passages. Each passage adds doublings, usually fewer as culture continues, and cells tend to become larger and flatter. Illustrative numbers, not Stem Nova lot data.

Why cell age matters in manufacturing

MSCs can be expanded many times, but not indefinitely. Wagner and colleagues described replicative senescence as a continuous process that begins with the first passage, with measurable changes in cell size, morphology and gene expression as culture continues. Bonab and colleagues reported that doublings per passage fell from about 7.7 early in culture to about 1.2 by passage 10 as cells slowed.

That is why expansion history is a quality question, not a marketing one. Two lots with the same cell count can come from very different points on this curve.

Illustrative only. There is no single doubling number that defines a good or bad lot; thresholds vary with tissue source, donor and culture method. Doubling count is not a universal quality score.

Reading it on the paperwork

  • Look for the number and the method. A passage number alone is incomplete; ask whether cumulative doublings were calculated and how cells were counted.
  • Match it to the lot. Expansion history should belong to the lot you are buying, not a typical value for the process.
  • Read it alongside viability and identity. Post-thaw viability, cell count and identity markers (the ISCT criteria) complete the picture.
  • Expect consistency. A well-controlled process produces similar expansion history lot after lot.

How Stem Nova applies it

Stem Nova tracks expansion through manufacturing and makes lot documentation available for review before purchase. Our 25M hUCT-MSC vial contains 25 million cells with 97% post-thaw viability. hUCT-MSC products are individualized and not FDA-approved; use is clinician-directed, and patients should consult their primary care provider.

What to ask your supplier

  1. What passage are the cells at harvest, and how many cumulative population doublings is that?
  2. How were cells counted at each seed and harvest?
  3. Is the expansion history specific to my lot, or a typical process value?
  4. What is the post-thaw viability and cell count for this lot, and who measured it?
  5. Do the cells meet ISCT identity criteria (CD73, CD90, CD105 positive; hematopoietic markers negative)?

Frequently asked questions

Is a lower doubling number always better?

Not on its own. Doubling count describes expansion history; it is not a universal quality score. It should be read with viability, cell count, identity markers and safety testing for the same lot.

Why do some suppliers report only passage number?

Passage number is simpler to track. It does not show how much cells divided within each passage, which is why cumulative population doublings are the more informative figure.

How are population doublings calculated?

For each passage, PD = log2(cells harvested ÷ cells seeded). Cumulative population doublings are the sum across all passages.

Does donor age matter as well as culture age?

Both are part of the picture. Donor age affects the starting cells, and culture expansion adds in-vitro age. The cord tissue page covers donor-source differences.

References

  1. Wagner W, Horn P, Castoldi M, et al. PLoS One. 2008;3(5):e2213. doi:10.1371/journal.pone.0002213. Cited for: replicative senescence across passages.
  2. Bonab MM, Alimoghaddam K, Talebian F, et al. BMC Cell Biol. 2006;7:14. doi:10.1186/1471-2121-7-14. Cited for: doublings per passage decline over serial culture.
  3. Dominici M, Le Blanc K, Mueller I, et al. Cytotherapy. 2006;8(4):315-317. doi:10.1080/14653240600855905. Cited for: ISCT minimal criteria for defining MSCs.
  4. Stolzing A, Jones E, McGonagle D, Scutt A. Mech Ageing Dev. 2008;129(3):163-173. doi:10.1016/j.mad.2007.12.002. Cited for: donor-age changes in bone marrow MSCs.

Citations support manufacturing, characterization and sourcing facts only. They are not claims about any Stem Nova product's effect in the body.

Source with the paperwork in hand

Licensed MD, DO, NP and PA practices can apply for wholesale access. Lot documentation is available for review, and applications are typically approved within 24 hours.

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For licensed medical professionals only. Exosome products are topical cosmetic products. hUCT-MSC products are individualized and not FDA-approved; use is clinician-directed, and patients should consult their primary care provider. Stem Nova Network does not provide dosing or procedural guidance. Products are not intended to diagnose, treat, cure, or prevent any disease. Stem Nova Network is a DBA of D1D Enterprises, Inc.