FDA Findings: Invalidating OOS Results Without Justification

An out-of-specification result is data. Invalidating it is allowed — but only when a laboratory error has actually been demonstrated. When a failing result is set aside because a retest passed, or because an error is possible, the batch decision is based on the results someone preferred, not on all the results. That is why OOS invalidation keeps appearing next to data integrity findings in Warning Letters.

Background: trial injections and testing into compliance.

What FDA found

Company X1 — no lab error, released anyway

Cited under 21 CFR 211.192. The letter states: “You invalidated the original OOS result with no identified laboratory error” for a stability assay; retests varied widely, and the batch was released before a root cause was identified. In a second case, a content uniformity OOS was confirmed by reanalysis, yet the firm still invalidated it and released the batch. FDA requested a retrospective, independent review of all invalidated OOS results for US products within expiry.

Company X2 — a passing hypothesis test used to erase a failure

Cited under 21 CFR 211.192. According to the letter, after a batch failed for unknown impurities, the firm tested a glassware-contamination hypothesis by preparing a second sample in glassware marked for disposal; it passed. FDA states the firm “still used the passing hypothesis test results as justification to invalidate” the original failing result.

Company X3 — new samples until it passed

Cited under 21 CFR 211.22. The letter states the firm invalidated multiple OOS results without adequate scientific justification, then prepared new samples and reported passing results; the QA-approved investigation did not explain why other samples in the same analysis were unaffected by the suspected contamination. FDA also noted hundreds of aborted chromatographic sequences without adequate trending or CAPA, and stated that “a possible laboratory error is insufficient to close an investigation at Phase 1.”

Why this happens

Interpretation — the letters state findings, not root causes. These are common patterns, not claims about these firms.

• Confusing “possible” with “proven”. Investigations list plausible causes (glassware, dilution, column) and treat the most convenient as confirmed.
• The retest decides. If a passing retest is allowed to overrule the original, the outcome is decided by how many attempts are made.
• Release pressure. An open OOS blocks a batch; a quick invalidation unblocks it.
• No trending. Without trending of invalidated OOS and aborted runs, a lab can’t see that “lab error” has become its most common result.

What good looks like

Example: a fictional QC lab with an OOS procedure aligned to FDA’s OOS guidance.

1. Phase I looks for an assignable, demonstrated error. An original result is invalidated only when the investigation identifies and documents a laboratory error with evidence — not a hypothesis. FDA’s data integrity guidance (question 2) requires a valid, documented, scientifically sound justification to invalidate a CGMP result.
2. Hypothesis tests test the hypothesis — not the batch. A hypothesis test is designed in advance to confirm or refute a specific cause. A passing result on a new preparation does not by itself prove the original was wrong.
3. Retesting is pre-defined. The number of retests, who performs them and how results are evaluated are set by procedure before testing — never “until it passes”.
4. No invalidation, no release. If no laboratory error is proven, the investigation extends to manufacturing, and the original result stands in the batch decision.
5. Trend invalidations and aborted runs. QA reviews the rate of invalidated OOS and aborted sequences by method, analyst and instrument. A rising rate is a signal, not a statistic.
6. Keep every result. All original, retest and hypothesis-test results remain in the record and are visible to the reviewer.

Perspective: what FDA’s requests tell you

Each letter asked for the same thing: an independent, retrospective review of invalidated OOS results — in X3 covering the three years before the inspection. That retrospective review is where the real cost of a weak OOS culture shows up. A lab that cannot defend its past invalidations has to re-examine every batch decision built on them. A strong OOS procedure is also a data integrity control: it is the mechanism that keeps unwanted results in the record.

Regulatory basis

• 21 CFR 211.192 — any unexplained discrepancy or failure of a batch to meet specifications must be thoroughly investigated, whether or not the batch has been distributed.
• 21 CFR 211.22 — quality control unit responsibilities.
• FDA guidance: Data Integrity and Compliance With Drug CGMP — Questions and Answers (December 2018), question 2 (when a CGMP result may be invalidated); and FDA’s guidance Investigating Out-of-Specification (OOS) Test Results for Pharmaceutical Production. Guidance is non-binding; the regulations are.

EU angle

Check current versions on EudraLex before relying on specific clauses. In EU GMP, OOS investigation expectations sit in EudraLex Volume 4, Part I, Chapter 6 (Quality Control).

Takeaways

• A possible error is not a proven error.
• A passing retest doesn’t erase a failing original.
• Define retesting before you test.
• Trend invalidations — they are a data integrity indicator.