Out-of-Specification and Atypical Laboratory Results

An out-of-specification result falls outside an approved acceptance criterion. An atypical or out-of-trend result may still pass but differs meaningfully from expected behavior.

Initial laboratory assessment

The laboratory should promptly assess:

• calculations
• sample preparation
• instrument status
• standards
• system suitability
• chromatographic integration
• transcription
• known deviations

Retesting

Retesting should follow a predefined plan. Repeated testing until a passing result appears is not scientifically acceptable.

Resampling

Resampling is appropriate only when the original sample may not represent the batch and the rationale is documented.

Manufacturing investigation

If no clear laboratory error is demonstrated, the investigation should extend to manufacturing, sampling, storage, and process history.

Frequently asked questions

Can one passing retest invalidate a failing result?

No. All valid results must be scientifically evaluated.

What is testing into compliance?

Repeating tests until a desired result is obtained without justified investigation.

Are atypical results important if they pass?

Yes. They can reveal process drift.

Should invalidated results be deleted?

No. They should remain traceable with documented justification.

Key takeaways

OOS and atypical results require structured, evidence-based investigation. The objective is to understand the result, not to replace it with a more convenient one.

References

1. FDA. Data Integrity and Compliance With Drug CGMP: Questions and Answers.
2. OECD Principles of Good Laboratory Practice.
3. ISO/IEC 17025 overview.

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TSMS Labs educational disclaimer: For laboratory research and educational purposes only. Not for human consumption. This content is not medical, clinical, or regulatory advice.