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OOS Investigation Template
Structured Out-of-Specification investigation following FDA's 2006 OOS Guidance. Complete Phase I laboratory investigation before proceeding to Phase II full investigation. Auto-saves locally. Print as PDF.
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Phase I — Lab Investigation
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Phase II — Full Investigation
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Frequently Asked Questions
An OOS (Out-of-Specification) result is any test result that falls outside the established acceptance criteria defined in the product specification, registration dossier, or official compendia (e.g., USP, EP). OOS results require formal investigation per FDA guidance and EU GMP. The investigation must determine whether the result represents a real product quality failure or is attributable to an identifiable laboratory error.
The FDA issued "Investigating Out-of-Specification (OOS) Test Results for Pharmaceutical Production" guidance in October 2006 (finalizing a 1998 draft). It describes a two-phase structured investigation: Phase I (laboratory investigation to identify assignable laboratory error) and Phase II (full investigation including manufacturing review, sampling assessment, and additional testing). The guidance explicitly prohibits discarding OOS results without scientific justification and sets strict limits on retesting.
OOS (Out-of-Specification) results exceed or fall below the defined acceptance limits. OOT (Out-of-Trend) results are within specification but show a statistically unexpected trend over time, detected through statistical process control or stability trending. OOT results indicate a potential developing quality problem. Both require investigation, but OOT investigations are proactive (before failure) while OOS investigations are reactive (after failure).
Yes, but only under strictly controlled conditions. An OOS result may be invalidated if — and only if — a specific, documented, assignable laboratory error is identified (e.g., wrong reference standard used, confirmed calculation error, documented instrument malfunction). Statistical outlier tests and lab retesting without identified cause are not acceptable for invalidation under FDA guidance. The original OOS result must always be retained in the analytical record.
Phase II is required whenever Phase I laboratory investigation concludes with no assignable laboratory error. Phase II extends the investigation to include: manufacturing records and process review, raw material verification, sampling procedure assessment, environmental monitoring data, and authorized additional testing. Phase II must be pre-planned, with the number of additional samples and testing criteria defined before testing begins.