This article in 30 seconds
- The name and the description alone cannot tell you what is inside. There is no official definition of the term "secretome (the totality of components a cell secretes during culture)," and some use the same word in a broader sense.
- "Serum-free" covers two different realities. A process that uses no serum at any step and one that switches to serum-free medium only for collection can both be described as "serum-free."
- When in doubt, start by requesting the lot-specific test reports. Whether the documents come out promptly shows you whether the supplier can answer the other points in writing as well.
Below, we first set out the six points to confirm in the form of questions, then use a figure to unpack the phrase that causes the most misunderstanding: "serum-free."
1. Why the name alone is not enough to compare
The short answer: there is no official definition of the term "secretome." Some use the same word in a broader sense, and at present the product name and description alone cannot tell you how the contents differ.
We therefore reserve the word "secretome" for products that meet all six of the criteria below, and in this article each criterion is recast as what to ask the supplier. The conceptual difference between conditioned medium and secretome itself is covered in Conditioned Medium vs. Stem Cell Secretome.
The key point
A product name works like a job title: on its own, it guarantees nothing about the contents. The one real test is whether the supplier can answer with numbers and documents. The six points below are a question list built for exactly that.
2. The 6 points to confirm with your supplier
In short, the six points confirm what is not added, what is measured, and what can be provided in writing. Each item below pairs what to confirm with what happens when it is not met.
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1Composed solely of components secreted by cells or tissue
- What to ask
- What is added during the collection step. Whether the composition of the culture medium can be disclosed.
- If not met
- The supplier cannot explain whether the values on the compositional data sheet are "what the cells secreted" or "what was added afterwards."
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2No cytokines or growth factors remaining from the collection medium
- What to ask
- Whether the collection medium is protein-free. Whether serum albumin or growth factors are added.
- If not met
- There is no way to tell whether the growth factors in the product came from the cells or were in the medium to begin with. It is like tasting a soup and not knowing whether the flavor is broth drawn from the ingredients or seasoning added at the start — the numbers turn ambiguous.
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3Contains proteins, peptides, nucleic acids, and membrane vesicles such as exosomes
- What to ask
- Whether exosome analysis (particle size and particle count) and protein quantification data are available.
- If not met
- Purification may have removed the very components you are after along with the impurities. "Clean" and "present" are separate claims, and each needs its own confirmation.
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4Free of harmful substances such as ammonia and heavy metals, and of impurities such as dead cells
- What to ask
- Whether reports for sterility testing, mycoplasma testing, and endotoxin testing come out for each lot. Whether results below the detection limit are shown as numbers.
- If not met
- The contents drift from lot (the unit manufactured at one time under the same conditions) to lot. The same product name can mean different contents with every delivery.
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5Manufactured without bovine serum
- What to ask
- Through which steps no serum is used. Is it avoided consistently from expansion culture through collection?
- If not met
- The conversation shifts to "how much was removed," and the supplier cannot answer "we do not use it." The next section explains this in detail.
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6Backed by compositional data
- What to ask
- Whether protein quantification, major cytokine measurements, and exosome analysis results can be provided — and whether they actually come out when requested.
- If not met
- You have no yardstick for comparing suppliers. And there is no way to verify whether the answers to points 1 through 5 are correct.
The key point
The six points are not equals: item 6, compositional data, is the key that unlocks the other five. If no documents come out, even the best answers to points 1 through 5 cannot be verified.
3. Which steps does "serum-free" actually cover?
Of the six, item 5 is the one wording alone can least settle. The short answer: the same phrase "serum-free" can describe two different realities.
One common approach uses serum-containing medium for expansion culture (the step in which cells are grown to the required number), then washes the cells and switches to serum-free medium only for collection. In the product description, this too can be written up as "serum-free."
The key point
Cells that spent expansion culture soaked in serum are like a sponge soaked in water. Rinsing the surface before collection does not rule out components absorbed inside seeping out later. "Washed out afterwards" and "never used at all" mean different things, even when both are written "serum-free."
So the question to ask is not "Is it serum-free?" but "Through which steps of the process is no serum used?" If no serum is used at any point from expansion culture through collection, the supplier can answer "we do not use it" without getting into removal rates.
For the design approach of what a culture medium deliberately leaves out, see Xeno-Free, Serum-Free, Protein-Free: What the Labels Mean. For why bovine serum components used in expansion culture cannot be fully removed downstream, see Bovine Serum RNA Cannot Be Fully Removed.
4. Where to start
If asking all six at once is impractical, we recommend starting with item 6, compositional data. The lot-specific test reports and compositional data are, so to speak, the product's medical checkup report. Without the report, there is no way to assess its condition at all.
Actually requesting them tells you a great deal on its own. Do they come out promptly? Are the values per lot, or representative figures shared across the product? What do the measured items include? Whether the answers to points 1 through 5 can be verified ultimately comes down to this.
For how to read what a test report actually covers, see Safety Testing of Conditioned Medium. For why price alone is a poor basis for comparison, see why "price per mL" is not a comparison metric (article in Japanese).
Frequently Asked Questions
Is a product safe to choose if it is labeled "serum-free"?
The label alone is not enough to judge. Cells can be expanded in serum-containing medium and switched to serum-free medium only for collection after washing — and that process can also be described as "serum-free." Confirm through which steps of the process no serum is used.
Which of the six points should we confirm first?
We recommend starting with the sixth: backed by compositional data. If you actually request the lot-specific test reports and compositional data, you will see whether the supplier has a system in place to answer the other points in writing as well.
Are these six points an industry-wide standard?
No. They are the definition we apply to our own products. There is no official definition of the term "secretome," and some use the word in a broader sense. Please use the six points as a yardstick for comparison.
This article explains manufacturing methods and how to verify quality control. Our stem cell secretome is supplied for research use only and is not intended to demonstrate efficacy against any specific disease.
We answer all six of these points in writing. To request test reports or compositional data, please contact us.
View Stem Cell Secretome specifications View our quality control system