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Understanding the "Passage Number"

The concept of "passage number" is central to cell culture and refers to the number of times a cell line has been subcultured or transferred to a fresh growth medium after its initial revival from cryopreservation or receipt from a reference cell bank. This metric is pivotal in tracking the lineage and history of a cell culture.

Process Overview

  • In routine cell culture practice, when cells attain a certain density, they are transferred to new medium to sustain growth and prevent overconfluence. Each such transfer is recorded as a passage.
  • Traditionally, when we received a cell line, for instance, at passage 60 from the depositor, we would continue from this passage number, incrementing with each subculture. This practice, while maintaining a historical thread, often led to high passage numbers from the outset. Given the extensive and often decades-long use of certain cell lines, such as the HeLa line established in 1951, it is not feasible to determine the total number of passages since the cell line's inception.
  • To enhance clarity and quality in our cell culture processes, we revised this approach at the beginning of 2023. Now, when we initiating a culture from a new vial, regardless of the passage number from the depositor, we reset and start counting anew from passage one for each manufactured batch.


Passaging is a vital procedure to ensure the health and utility of cell cultures for research. When cells become overgrown, they experience contact inhibition, reducing their proliferation rate, which can adversely affect experimental outcomes. To mitigate these issues, Cytion implements stringent controls over the cell densities at which subculturing occurs, thereby maintaining low passage numbers during the manufacturing of their cell lines. This precaution helps prevent the adverse effects of excessive passaging, such as morphological anomalies, growth rate changes, and genetic drift, which may cause the cells to differ markedly from their original state. Extended periods of subculturing can also heighten the risk of microbial contamination.

Our Promise

We ensure that the cells supplied to researchers are as close to the original genetic makeup and phenotypic characteristics as possible, enhancing the reliability of experimental data. Furthermore, by documenting each passage meticulously, Cytion contributes to the traceability and reproducibility of research, a commitment that reflects the high standards of practice in cell culture. Researchers are encouraged to maintain accurate records of passage numbers, both on the culture vessels and in their lab notebooks, as a reference for the health and history of their cell cultures.

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