Sterility Testing Under USP <71>
How membrane filtration sterility testing works, why it takes fourteen days, and what the result actually covers.
How does USP <71> sterility testing work?
The contents of intact unopened units are dissolved and passed through a membrane filter fine enough to retain micro-organisms. The membrane is rinsed, divided, and transferred into two growth media: fluid thioglycollate for anaerobes and soybean casein digest for aerobes and fungi. Both are incubated for fourteen days and examined for growth.
The fourteen days are not laboratory scheduling. They are the incubation period the method requires, because slow-growing and stressed organisms may take that long to become visible.
Frequently asked questions
- Why does sterility testing take 14 days?
- Because that is the incubation period the compendial method specifies. Some organisms grow slowly, and organisms stressed by lyophilisation or by the filtration process itself can take considerably longer to become visible than they would from a healthy culture. A shorter incubation would produce faster answers and a higher false-pass rate, which is why expedited processing cannot compress it.
- Can sterility testing be done on an opened vial?
- No, not meaningfully. Sterility asks whether viable organisms are present in a sealed container. Once that container has been entered for any purpose, any subsequent growth cannot be attributed to the original contents rather than to the act of entry. A result from a previously sampled vial would be uninterpretable regardless of whether growth occurred.
About the author
REPLACE: Microbiology Lead
Head of Microbiology · MSc Microbiology
Placeholder profile for the analyst who owns sterility and bacterial endotoxin testing. Replace with the real person before launch.
Have a sample that needs characterising?
Build a submission online and see an itemised estimate as you select assays. Every result is reported exactly as measured.
Related reading
Submission Guidance
Why Sterility and Endotoxin Need Dedicated Vials
The chain-of-custody reason these assays cannot share material, and how to count vials before shipping.
Analytical Methods
Bacterial Endotoxin Testing Explained
How the LAL assay quantifies endotoxin burden, what EU per milligram means, and why the test needs its own vial.
Analytical Methods
Peptide Testing Methods Explained
How each instrument works, what it can measure, and where its limits are. Written for people commissioning the work, not operating it.