Before a sample of adipose tissue enters long-term storage, a laboratory has to answer three narrow questions. Is it sterile. Is it free of bacterial endotoxin. Is it free of mycoplasma. Sterility testing in adipose tissue banking is not one assay but a release panel, and each part carries its own method, its own clock, and its own pass or fail line.
TLDR: Release testing rests on three assays: sterility under USP chapter 71, tied to the federal sterility rule at 21 CFR 610.12; endotoxin by Limulus amebocyte lysate; and mycoplasma by culture or PCR. Compendial sterility takes 14 days to read and mycoplasma culture at least 28, so frozen material is easier to release than a fresh preparation with a 48 to 72 hour shelf life. Post-thaw viability varies with what was frozen and how. Adipose tissue and stromal vascular fraction are investigational and not FDA approved, and banking cannot guarantee eligibility, access, or clinical benefit.
Important Disclaimer: Save My Fat is a connector linking patients and providers to a United States tissue bank. It does not provide FDA-approved treatments or cures and does not guarantee eligibility, access, or clinical benefit. Release testing confirms a stored sample met defined safety criteria on a given date, nothing more. This article is for educational purposes only, and readers should consult their own licensed healthcare professionals before making decisions about tissue banking.
Patients tend to picture banking as a freezer problem. Get the sample cold, keep it cold, and the work is done. The freezer is the straightforward part. The demanding part happens between collection and the moment a sample is formally released into inventory.
In that window a laboratory has to show the material is not carrying something it should not. The proof is a set of named tests with published methods and stated limits. They measure contamination, not whether cells will ever be useful.
Sterility Testing in Adipose Tissue Banking Is a Panel, Not One Test
Three assays carry most of the weight in safety testing before tissue storage. Jha, Farnoodian and Bharti described the release testing framework for cell products in Stem Cells Translational Medicine in 2021, and the same three recur across published specifications.
Sterility Under USP Chapter 71
Sterility is assessed under United States Pharmacopeia chapter 71, the compendial sterility test, tied to the federal sterility requirement at 21 CFR 610.12. The question is binary. Sample material goes into growth media, the media is incubated, and a reader records whether anything grew. There is no partial credit.
Bacterial Endotoxin by Limulus Amebocyte Lysate
Endotoxin is not an organism. It is a fragment of the outer membrane of gram-negative bacteria, and it persists after the bacterium is dead. A sample can pass sterility and still fail an endotoxin limit. The Limulus amebocyte lysate assay reports endotoxin units per milliliter against a stated maximum.
Mycoplasma by Culture or PCR
Mycoplasma are very small bacteria with no cell wall. They slip through filters that stop other organisms and do not cloud culture media, so a contaminated preparation looks entirely normal. Detection is by culture or PCR, and culture is the older, slower reference method.
A Real Tissue Bank Release Testing Specification
Release criteria stay abstract until you see a set written down. Phermthai and colleagues published a release specification in Stem Cell Research and Therapy in September 2025 that puts the panel in three lines, each naming a test, a method, and the criterion a lot must meet.
| Test | Method | Release criterion |
|---|---|---|
| Bacterial endotoxin | Kinetic turbidimetric LAL | Less than 0.5 EU/mL |
| Mycoplasma | PCR | Negative |
| Sterility | USP chapter 71, direct method | No growth |
Only one line carries a number. The other two are absolute, which is the usual shape of tissue release criteria.
The 14 Day Clock, and Why Banked Tissue Is Not Racing It
Timing separates banked material from same-day processing more sharply than anything else. Guadix and colleagues set out the arithmetic in a 2019 review in Pharmaceutics. Compendial sterility requires a 14 day incubation. Conventional mycoplasma culture requires at least 28 days.
Set that against a fresh, non-cryopreserved cell preparation, which carries a shelf life of 48 to 72 hours. The product is used and gone before the sterility incubation finishes, so the final result arrives after the fact unless rapid methods are substituted.
Cryopreserved banked tissue does not sit under that clock. It stays frozen while incubations run to completion, so a full compendial result can be read before anything leaves quarantine. That is a real advantage of banking over same-day processing, and it is worth naming precisely: it is time to finish a test, not evidence that stored tissue will ever be useful. Adipose-derived products remain investigational and are not FDA approved.
What Post-Thaw Viability Numbers Actually Show
Viability is the other number on a release record, and the one most often quoted with no context. It is not a fixed property of frozen fat. It depends on what was frozen, the cryoprotectant, the cooling rate, and the storage temperature.
Thirumala and colleagues reported roughly 84 percent post-thaw viability for passaged adipose-derived stromal cells in Stem Cells and Development in 2010. Their companion study of stromal vascular fraction cryopreservation found about 63 percent with 10 percent DMSO plus serum. The stromal vascular fraction is the more fragile of the two.
| What was cryopreserved | Reported post-thaw viability | Source |
|---|---|---|
| Passaged adipose stromal cells with DMSO | About 84 percent | Thirumala, Stem Cells and Development, 2010 |
| Stromal vascular fraction, 10 percent DMSO plus serum | About 63 percent | Thirumala, J Tissue Eng Regen Med, 2010 |
| Stromal vascular fraction, 10 percent PVP | About 54 percent | Thirumala, same series |
| Fraction held overnight at plus 4 C before freezing | 11.6 percent lower | Agostini, Stem Cell Research and Therapy, 2018 |
| Whole cryopreserved fat, fraction measured | 42.6 and 55.4 percent, against 90.6 percent fresh | Mashiko, Plastic and Reconstructive Surgery, 2018 |
| Fat frozen at minus 20 C | Not viable | Moscatello, Dermatologic Surgery, 2005 |
Read the middle column top to bottom. The spread between rows is wider than the spread between donors, so method matters more than the patient.
The Adipocytes Largely Do Not Survive
The most consequential row is Mashiko. Working with whole cryopreserved adipose tissue, that group measured stromal vascular fraction viability of 42.6 percent and 55.4 percent against 90.6 percent for fresh tissue, and reported that most adipocytes were necrotic.
State that plainly, because the misunderstanding is common. In banked whole adipose tissue the fat cells themselves largely do not survive freezing. The stromal vascular fraction and adipose stromal cell compartment do survive, at reduced viability. Anyone picturing intact fat coming back out of the tank the way it went in has the wrong model.
Protocol Explains More Than Tissue Does
Moscatello and colleagues showed what a wrong protocol produces. Reporting in Dermatologic Surgery in 2005, they found fat frozen in an ordinary freezer at minus 20 degrees Celsius was not viable. Viable cells came back only with a cryoprotectant, controlled-rate freezing at 1 degree Celsius per minute, and nitrogen vapor storage.
Duration matters less than people expect. Agostini and colleagues found overnight storage at plus 4 degrees Celsius cut viability by 11.6 percent, while viability was not significantly affected after a year frozen. Devitt and colleagues, in Stem Cells International in 2015, examined storage from 2 to 1159 days and recovered more viable cells initially from tissue frozen under a year than over two years, though that difference did not persist with continued growth. Broader cryopreservation viability data follows the same pattern.
Where State Law Picks Up the Viability Number
Florida requires a report but not a number. Its law, effective July 1, 2025, requires that a product contain viable or live cells upon post-thaw analysis and that a post-thaw viability report for the product lot reach the physician before use. It sets no numeric threshold.
Tennessee is the only state that sets numbers. Public Chapter 1016, effective July 1, 2026, requires greater than 90 percent viability on a pre-thaw certificate of analysis and no less than 80 percent on a post-thaw viability analysis report, unless the product is autologous. Georgia’s law, also effective July 1, 2026, requires neither.
Hold Tennessee’s 80 percent floor against the table above. Passaged adipose stromal cells at about 84 percent clear it. Stromal vascular fraction at about 63 percent does not. Whole cryopreserved fat at 42.6 and 55.4 percent is nowhere near it. That autologous carve-out does real work, since a patient’s own banked material would often fail a threshold written for donor products.
What Happens When a Sample Fails
A failed release test is not a judgment call, which is the point of writing criteria down in advance. Growth on sterility, a positive mycoplasma result, or endotoxin above the limit is a fail, and the lot does not enter released inventory. Current Good Tissue Practice, Subpart D of 21 CFR Part 1271, covers establishments handling human cells and tissues, and facilities working to those good tissue practice rules build testing into a documented process.
What a patient should see is paperwork. A certificate of analysis naming each test, method, criterion, and result. The date each test was run. Storage conditions. And a chain of custody record tying the sample in the tank to the person it came from.
Frequently Asked Questions
What specific tests are performed on tissue before it is approved for long-term storage?
Three form the core panel: sterility under USP chapter 71, endotoxin by Limulus amebocyte lysate, and mycoplasma by culture or PCR. A published 2025 specification set endotoxin below 0.5 EU/mL by kinetic turbidimetric LAL, mycoplasma negative by PCR, and sterility with no growth.
What is sterility testing and why is it required?
Sterility testing asks whether viable microorganisms are present. Material goes into growth media, is incubated, and is read for growth. The compendial method is USP chapter 71, tied to the federal sterility requirement at 21 CFR 610.12. Contaminated material carries infection risk no later step undoes.
What happens if a tissue sample fails a safety test?
The lot fails and does not move into released inventory. Criteria are written before testing precisely so the answer is not negotiable afterward. Growth on sterility, a positive mycoplasma result, or endotoxin over the limit each stand alone. The event belongs in the record.
How does this testing relate to Current Good Tissue Practice requirements?
Subpart D of 21 CFR Part 1271 sets Current Good Tissue Practice, the federal framework for establishments handling human cells and tissues. Release testing is one visible output of operating under it. Testing, records, and storage conditions are expected to form a documented, traceable system.
What documentation should patients expect about their tissue’s testing results?
Ask for a certificate of analysis listing each test, method, acceptance criterion, and result, with dates. Ask for storage conditions and the chain of custody record connecting the stored sample to you. If viability was measured, ask for that number and its method.
Why does cryopreserved tissue avoid the timing problem fresh preparations face?
Compendial sterility takes 14 days to read and conventional mycoplasma culture at least 28, while a fresh non-cryopreserved product has a 48 to 72 hour shelf life. Fresh material can be used before final results exist. Frozen material waits, so testing finishes first.
Key Takeaways
Release testing before storage rests on three assays: sterility under USP chapter 71, tied to 21 CFR 610.12, endotoxin by Limulus amebocyte lysate, and mycoplasma by culture or PCR. One published 2025 specification set endotoxin below 0.5 EU/mL, mycoplasma negative by PCR, and sterility with no growth. Compendial sterility needs 14 days and mycoplasma culture at least 28, so a fresh product with a 48 to 72 hour shelf life can be used before results exist, while frozen material simply waits.
Viability deserves more caution still. Passaged adipose stromal cells run near 84 percent, stromal vascular fraction near 63 percent, and whole cryopreserved fat has been measured at 42.6 and 55.4 percent with most adipocytes necrotic. The stromal compartment survives freezing far better than the fat cells, and protocol drives that more than biology.
Save My Fat operates as a tissue preservation service, not a medical practice or treatment provider. Stem cell and regenerative medicine regulations vary by state, including specific informed-consent and disclosure requirements in Florida, Utah, California, Georgia, and Tennessee governing tissue and stem cell services. Banking adipose tissue does not connect patients to any treatment pathway, and any future use depends on FDA regulatory status, physician guidance, and the availability of approved or investigational pathways at that time.
Patients considering adipose tissue banking for potential future use can review current pricing or bring documentation questions to the Save My Fat team.
Save My Fat works with a U.S.-based tissue bank for laboratory processing and storage.
This article is for educational purposes only and does not constitute medical or legal advice. Legal and medical review including neurology and neurosurgery input is required before publication. Please consult your neurologist or neurosurgeon before making any decisions about banking, treatment, or research participation.
About the author: Oscar Tellez is the founder and CEO of Save My Fat. He holds a Bachelor of Science in Exercise Science and Health Promotion from Florida Atlantic University. He has spent more than a decade in the regenerative medicine industry across product distribution, laboratory and vendor relationships, and provider training. He is not a licensed clinician, and this article is educational, not medical advice.
Related guide: FDA adipose tissue regulation.
