Forty-eight hours after an injection that the procedure note described as “uneventful,” the patient sits at the kitchen table with a single sheet of paper that arrived in the discharge folder. The page has the clinic letterhead, a date, a procedure code, and four numbers. Total cells delivered. Cell viability percentage. Cell type identification, with a brief notation. Sample processing time. The patient does not know whether the four numbers are good numbers, average numbers, or numbers that should have prompted a question before the injection rather than a question forty-eight hours after.
This guide is for that moment. It is for the patient who already received the report and wants to understand what they have. It is for the reader who has not yet received one and wants to know what to ask for. It is also for those whose clinic does not produce a report at all, since that absence is itself a piece of information worth understanding.
What Documentation Patients Should Expect (and What to Ask If It Is Not Provided)
A report from a quality cell-processing operation tends to include a short list of items. The list runs roughly the same across same-day autologous concentrate procedures and culture-expanded products, with longer expansion-specific addenda for the latter:
- Total cell count delivered, expressed as a number or per-milliliter concentration in the final product
- Cell viability, expressed as a percentage of live cells at the time of preparation or shipment
- Cell type identity, where the product type calls for it, reported through surface marker analysis or a comparable identity assay
- Sample processing time from harvest to reinjection
- Sterility testing result, particularly for products that spend any time outside the patient’s body in a culture environment
- For expanded products, passage number and any potency or functional assay results required by the lot release criteria
When a clinic provides this list without prompting, the documentation is operating at the level the AABB Standards for Cellular Therapy Services describe. When a clinic provides only a procedure note and no analytical numbers, the patient’s first follow-up question is whether the numbers exist at all and, if so, whether they can be sent. A clinic that runs the assays generally documents them. A clinic that does not run the assays often does not document them, and asking tends to clarify quickly which situation applies.
A short note for the reader who is not sure whether to push: most quality clinics treat the request as routine. The request itself does not imply mistrust. It indicates that the procedure is being read as a clinical event rather than a customer-service event, which is the position the consultation should have established from the first appointment.
What Cell Count Tells You About Your Treatment
Cell count is the most common number on a viability report and the most often misread. The number describes how many total cells were delivered to the target site, or sometimes how many cells per milliliter were present in the final product. Both formats are legitimate. The two are not interchangeable, and a report that gives one without context can mislead a patient who is comparing two clinics that report differently.
A few practical points worth carrying:
- Total cell count tends to be more useful for comparing across procedures, since it reflects the dose actually delivered.
- Per-milliliter concentration tends to be more useful for understanding the product itself, but it does not indicate how much volume was injected.
- Higher cell counts do not automatically translate to better clinical response, since the relationship between dose and effect is condition-specific and often non-linear.
- Therapeutic dose targets in clinical trials, when reported in the published literature, often run in the millions or tens of millions of cells per injection, depending on cell type and target tissue.
A patient comparing two reports who sees vastly different numbers should ask which format each clinic uses, what volume each delivered, and what target dose the clinic considers therapeutic for the specific condition. The answer often tends to clarify what looked like a meaningful difference into a unit-of-measurement difference.
Viability Percentages: Reading Them in Context
Cell viability, on a quality report, runs as a percentage. The number describes how many of the cells in the final product were alive at the time of measurement, as opposed to dead, dying, or otherwise non-viable. The most common method is dye exclusion using trypan blue, where dead cells admit the dye and live cells exclude it. Flow cytometry can produce a more refined viability number using fluorescent markers. Both methods are recognized by AABB and ISCT framework documents.
Practical context for the percentage:
- Quality cell preparations for clinical use often report viability in the range commonly described in the literature as “high viability,” with specific thresholds set by lot-release criteria for the product type.
- A viability number reported without a measurement timepoint is less informative than a viability number reported with the time of measurement and the time of injection, since cells lose viability between preparation and injection.
- Viability and potency are not the same concept. A high-viability product can still have low potency if the cells, while alive, do not perform the intended biological function. The FDA Potency Tests for Cellular and Gene Therapy Products final guidance treats potency as a separate release criterion, which means seeing only a viability number means seeing one part of a larger framework.
- Viability of dead cells is zero. Reports that describe an unusually low viability number should prompt a conversation about the time-course of the measurement, the storage conditions, and whether the product met release criteria for use.
The patient comparing two reports often tends to focus on the viability percentage first because it looks the most like a familiar grade. The number is meaningful. It is also one input among several that together describe what the cells could be expected to do.
Why Cell Type Identification Matters in the Report
Cell type identification, where the product specification calls for it, is the report section most patients skim first and understand last. The section names what the cells are. For mesenchymal stromal cell products, the ISCT minimal criteria specify a positive marker profile (CD105, CD73, CD90 in defined percentages) and a negative marker profile (CD45, CD34, CD14 or CD11b, CD79α or CD19, and HLA-DR), along with functional assays that have evolved through the 2006 position statement and subsequent committee revisions.
What appears on the report is usually a short notation. What underlies the notation is the full identity panel the lab ran on the lot. Asking for the panel is asking a question the lab is set up to answer in writing. If the report names the cells but does not specify which markers were measured or what percentages were observed, the patient has identified a useful follow-up question for the next consultation.
Three practical implications for the patient:
- Cell type identification matters more for culture-expanded products than for same-day concentrates, since expansion can shift the cell population over passages.
- A product marketed as “stem cells” that does not specify cell type or surface marker panel may be operating at a vocabulary level rather than a specification level.
- A product marketed as “MSCs” should meet the ISCT minimal criteria, and the report should make the criteria match visible.
How Sample Processing Time Shapes Report Numbers
Time matters in cell biology in ways the report itself often does not narrate. From harvest to reinjection, cells lose viability gradually if not held in appropriate conditions. From measurement to injection, the viability number on the report can shift if storage time runs longer than expected. The report’s processing time field, when present, clarifies whether the numbers describe the cells as they entered the product or as they were delivered to the target tissue.
A short reference for time-related questions:
- Same-day autologous procedures typically have processing windows in the range of one to three hours from harvest to injection.
- Culture-expanded products have processing chains running days to weeks, with cold-chain or controlled-temperature storage between manufacture and shipment.
- Allogeneic donor products that ship from a tissue bank have transit time as part of the chain, and the report’s storage condition and time-of-measurement notation often tend to be the most useful detail.
- Older numbers often describe the cells better at the moment of preparation than at the moment of injection. The two can differ. The difference depends on storage protocol.
When a clinic’s report includes time-of-measurement and time-of-injection separately, the patient is reading documentation built for the question. When the report includes only one timepoint, the patient asking which timepoint the number describes is asking the question the report should have answered up front.
Where Reports Compare and Where They Differ
A patient evaluating two clinics by their reports is comparing apples and apples, mostly, with occasional pears. The dimensions where reports compare cleanly:
- Cell count, when both reports use total delivered cells in the same volume context
- Viability percentage, when both reports specify the measurement method and the timepoint
- Sterility testing, when both reports include the result and the assay type
- Cell type identification, when both reports cite the same identity panel
The dimensions where reports tend to differ in ways the patient should notice:
- Reporting format, since some clinics produce a structured certificate of analysis and others produce a procedure note with embedded numbers
- Lot release criteria, since culture-expanded products carry release criteria that bench-side concentrates do not
- Functional or potency assay inclusion, since the FDA framework treats potency as a separate criterion for products in the Section 351 pathway, and reports for Section 361 products often do not include the same functional data
- Documentation completeness, since clinics that operate under more rigorous quality systems often produce more detailed reports
Forty-eight hours after the procedure, the patient at the kitchen table reads the four numbers differently than they read them when the discharge folder arrived. The total cell count has a unit that matches what the consultation described. The viability percentage carries a measurement method and a timepoint. The cell type identification matches the product type the consultation discussed. The processing time runs in a window the literature describes as standard for the procedure. None of the four numbers is a guarantee. All four together describe a product the patient can discuss in operational terms with the next clinician they see. That capacity to have the operational discussion is often what the consultation and the documentation together are meant to make possible.
Important note on cell-source decisions: No cell-source or processing approach removes the regulatory framework risk, and FDA distinctions between 351 and 361 products affect what clinics may legally offer. The realistic question is what documentation the patient asks for and what specific practices verify a clinic operates within current FDA guidance.
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