Microbiological safety · O-021
Sterility, endotoxin and microbial testing
A purity result does not cover microbiological risk. Sterility, bacterial endotoxin, bioburden and particulate contamination are separate attributes with separate methods and sampling limits.
Sterility testing examines whether viable contaminating microorganisms are detected under a defined pharmacopoeial procedure, while bacterial endotoxin testing measures endotoxin from certain bacteria. Neither result can be inferred from HPLC purity, mass spectrometry identity or a clean-looking vial, and the absence of these tests leaves the relevant safety attributes unknown rather than passed.
Research-grade certificates often omit microbiological quality tests because the material was not released as a sterile medicine. That omission does not make an untested product suitable for injection or any other human use.
Which test answers which question?
| Attribute | Question | Important limit |
|---|---|---|
| Sterility | Were viable microorganisms detected under the specified test conditions? | A sample-based test cannot prove absolute absence in every unit |
| Bacterial endotoxin | Was endotoxin detected or quantified by the stated method? | It does not detect every pyrogen or viable microorganism |
| Bioburden | How many viable microorganisms were present before a sterilising step or in a non-sterile material? | It is not a sterility claim |
| Particulate contamination | Were visible or sub-visible particles assessed by the specified procedure? | A clear vial can still contain sub-visible particles |
What does a missing result mean?
If a certificate does not list sterility or endotoxin testing, read the document as silent on those attributes. Do not convert silence into “not detected”, “passed” or “safe for use”.
A seller may describe a material as high purity while providing no microbiological evidence. Both statements can be true because chemical purity and microbiological quality occupy different parts of the evidence record.
What should the laboratory report?
- Named procedureThe report should identify the pharmacopoeial or validated method and any justified alternative.
- Sample and batchThe tested units, batch reference, receipt condition and preparation need traceability.
- SpecificationA result needs the acceptance criterion that the laboratory applied.
- Method suitabilityThe sample must not inhibit or enhance the test in a way that makes the result unreliable.
- DeviationsAny compromised container, growth interference, invalid run or repeat should appear in the controlled record.
What should someone do after a suspected reaction?
Anyone who becomes unwell after using an experimental or unauthorised product should seek medical advice and report the suspected reaction through the Yellow Card route. Severe breathing difficulty, collapse, confusion or rapidly worsening symptoms require urgent NHS help through 999 or A&E.
Continue the evidence check
Read research-use-only limits
Understand why a research certificate may omit medicine-release tests.
Questions readers ask
Does an HPLC pass mean a peptide is sterile?
No. HPLC evaluates chromatographic behaviour under its stated method. Sterility and bacterial endotoxin require separate microbiological procedures. If the certificate does not name those tests and results, the product's microbiological safety remains unknown.
Are sterility and endotoxin the same test?
No. A sterility test looks for viable contaminating microorganisms under defined conditions. A bacterial endotoxin test measures endotoxin associated with certain bacteria. A product can meet one criterion and fail another, so each result must appear separately.
Can a sterility test prove every vial in a batch is sterile?
Sterility testing samples a limited number of units and cannot prove absolute absence across every vial. Confidence depends on controlled manufacturing, validated sterilisation or aseptic processing, environmental monitoring, container integrity, sampling and release testing.
What does “not tested” mean?
It means the certificate provides no result for that attribute. It does not mean “not present”, “not required for human use” or “safe”. Research-use labelling may explain the omission, but it does not create evidence of microbiological quality.
Primary sources and update triggers
- EDQM: Pharmacopoeial harmonisation status: current references for chromatography, sterility and bacterial endotoxin chapters
- UKAS: Laboratory accreditation and ISO/IEC 17025: competence, impartiality and consistent operation within a defined testing scope
- EMA: ICH Q2(R2) Validation of Analytical Procedures: validation for identity, assay, purity, impurities and other intended analytical purposes
Editorial experience
From our work: how we checked this page
For topical-map item O-021, Sterility, endotoxin and microbial testing was checked as a distinct editorial task, not treated as a generic peptide page. We reviewed 3 unique external sources and 8 internal destinations in the page, then checked that the opening answer, headings, source descriptions and linked next steps stayed within the same claim boundary. The count records links in the published page and is not a claim that every source carries equal evidential weight.
Eleni Kiromitis checked the laboratory and scientific wording, drawing on direct experience commissioning laboratory tests and reviewing certificates of analysis and chromatograms. She checked whether each method was matched to the attribute it can measure, whether sample and batch limits remained visible, and whether the conclusion stopped where the analytical record stopped. Yianni Kiromitis retained responsibility for source verification, editorial decisions and correction management.
We did not use patient experience, a personal treatment outcome, seller testimony or an assumed product identity to support this page. The publication did not independently test a vial for this review. Where a page refers to a laboratory result, that result applies only to the named sample, method and attribute. We kept uncertainty beside the conclusion, recorded which source supports each material claim, and checked that the visible review date matches the publication record. A new controlled study, regulator update, corrected source, analytical report or credible safety signal can trigger reassessment through the public correction route.