What happens when a peptide test result is out of specification?
An out-of-specification (OOS) result is a test result that falls outside the acceptance criteria, for example HPLC purity below 99%. Good practice requires a documented investigation: first check for laboratory error, then, if none is found, investigate manufacturing. Retesting until a pass appears, or averaging a failure away, is not acceptable.
What counts as OOS, OOT and atypical?
- OOS (out of specification): outside the acceptance criteria.
- OOT (out of trend): within specification but inconsistent with previous results, for example in a stability series.
- Atypical result: unexpected but not failing, such as an unusual extra peak.
- Only OOS automatically triggers a formal failure investigation; the others are judged case by case.
How is an OOS result investigated?
The FDA guidance on investigating OOS results sets out this phased approach and is the most widely cited reference for laboratories worldwide.
| Phase | Question | Typical checks |
|---|---|---|
| Phase I (laboratory) | Was it a lab error? | Calculations, instrument, standards, sample preparation, analyst interview |
| Phase II (full-scale) | Is the material really failing? | Manufacturing records, retest by a second analyst under a written protocol |
| Conclusion | Invalidate or confirm | Document root cause; reject the lot if confirmed |
Source: FDA: Investigating Out-of-Specification (OOS) Test Results
Can a failing result simply be retested?
Only under a predefined plan and with a stated reason. The guidance warns against 'testing into compliance': repeating tests until one passes and reporting that one. Averaging is also restricted, because a mean can hide an individual failing result.
What does this mean for a CoA?
- A CoA shows the reportable result, not the investigation history.
- Ask whether the lab has a documented OOS procedure.
- A supplier that releases lots against a fixed specification, such as ≥99% HPLC purity, should reject lots that fail it.
How does Sable handle release?
Lots are released only at ≥99% HPLC purity with identity confirmed by mass spectrometry. There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Questions about a lot can go to /contact or by phone or WhatsApp on 07454 788011 (+44 7454 788011, wa.me/447454788011).
Frequently asked questions
What is an OOS result?
A test result outside the specification's acceptance criteria, such as HPLC purity below the stated limit.
What is the difference between OOS and OOT?
OOS fails the specification; OOT is within specification but out of line with the trend of earlier results.
Can a lab retest until it gets a pass?
No. Retesting must follow a predefined protocol with a documented reason; 'testing into compliance' is not acceptable.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- OOS = outside acceptance criteria
- Phase I lab investigation → Phase II full investigation
- Reference: FDA OOS guidance
- Updated 2026-10-16