Testing desk · Method explainer
Sterility testing: what it detects and what a ‘pass’ means
How sterility testing works (compendial culture vs rapid PCR methods), what a pass does and doesn't prove, and how it differs from endotoxin testing.
The short answer ·
Sterility testing looks for viable microorganisms (bacteria and fungi) in a sample. Compendial tests incubate the sample in growth media for about two weeks; rapid methods, including PCR-based screens, detect microbial DNA or signals faster. A pass means no contamination was detected in the units tested, not that every vial in the lot is sterile.
It does not measure endotoxin.
How is sterility tested?
| Compendial culture (e.g. USP <71>) | Rapid / PCR-based | |
|---|---|---|
| Principle | Sample in growth media; watch for growth | Detect microbial DNA or metabolic signals |
| Time | About 14 days of incubation | Hours to days |
| Detects | Viable organisms that grow in the media | Organisms whose DNA/signal the assay targets; may also detect DNA from dead cells |
| Typical use | Regulated sterile drugs | Screening; some consumer-facing peptide labs |
Freedom Diagnostics lists “Sterility (PCR)” as its method. Chromate’s sample instructions say additional vials are needed for microbiology tests beyond the one used for HPLC.
What does a sterility pass mean?
Sterility testing is statistical. Testing a few units can miss low-level contamination across a lot. A “pass” on one vial means that vial showed no detected contamination by that method. It says nothing about the next vial, or about handling after opening.
Is sterility the same as endotoxin?
A sample can pass sterility and still carry endotoxin from bacteria killed during processing. The two tests answer different questions (endotoxin explainer).
How do you read sterility on a report?
- Method named (culture or PCR) and organisms targeted
- Number of units tested
- Sample lot matching the purity/identity tests
- Negative and positive controls noted
Frequently asked questions
Is lyophilized peptide powder sterile?
Not necessarily. Sterility depends on how it was manufactured and filled. Only testing, ideally of multiple units, gives evidence, and it is still a sample.
Is a PCR sterility test the same as the USP test?
No. PCR screens detect microbial DNA and can be faster, but they are a different method from compendial culture-based sterility testing. A report should say which was used.
Sources
3 linked records- [1] Freedom Diagnostics Testing: Sterility (PCR) Freedom Diagnostics Testing Primary record
- [2] Chromate: sample preparation (additional vials for microbiology) Chromate Primary record
- [3] FDA Pyrogen and Endotoxins Testing Q&A U.S. FDA Primary record
This explainer is general information about law and laboratory methods, not legal or medical advice. Amino Wire does not provide dosing information. Spotted an error? See our corrections policy.