OOS Investigation
An OOS investigation is not defensible because testing was repeated. It is defensible when the record explains the conclusion.
For an out-of-specification result, a later reviewer should be able to see what evidence was evaluated, why a laboratory or manufacturing cause was accepted or rejected, what uncertainty remained, and how the final disposition was authorized.
The decision boundary
The consequential decision is the conclusion—not merely the sequence of tests.
Why did the available evidence support this root-cause conclusion and the resulting batch disposition?
What the record should make reviewable
Evidence
Original result, raw data, method and instrument review, analyst observations, sampling and production evidence, historical patterns, and relevant retest data.
Judgment
Why the evidence supports or does not support laboratory error, manufacturing cause, assignable cause, invalidation, retesting, or another investigation conclusion.
Risk & authorization
Impact on affected and potentially affected batches, residual uncertainty, CAPA implications, and the accountable Quality authorization for the final disposition.
FDA context
Use the FDA OOS guidance as the regulatory reference point.
FDA describes OOS results broadly as test results outside specifications or acceptance criteria, including in-process laboratory tests. When an initial assessment does not establish laboratory error and the result appears accurate, the guidance describes a full-scale investigation intended to identify root cause and appropriate corrective and preventive action.
Preserve the conclusion
If the OOS decision is challenged later, the record should answer without reconstructing the investigation.
Use the DDA on one completed OOS decision, or review the OOS scenario to see the questions a later reviewer may ask.