A passing retest does not automatically erase a failing lab result

Read beyond the final result

When reviewing peptide documentation, a replacement PASS raises an important question: what happened to the original result? FDA's pharmaceutical-testing guidance explains why retesting needs an investigation, not simply repeated attempts until something passes.

Four useful takeaways

• Retesting should follow a scientifically justified plan, with limits established in advance.
• Without an identified laboratory or calculation error, passing retests do not justify invalidating the original out-of-specification result.
• When a laboratory error is established, the original data should still be retained with a documented explanation.
• An initial failure does not automatically condemn a batch. The investigation and complete results matter.

FDA OOS guidance, sections IV.B.1 and V.A

Put the evidence in context

Ask whether the laboratory can explain the discrepancy and provide the investigation, not just the replacement certificate. This is our document-review recommendation, not a finding about any supplier.

This source addresses pharmaceutical production. It does not certify research peptides or establish product safety, efficacy, approval, or suitability for human use. We make no allegation about any vendor.

A question for your next review

If two reports disagree, what evidence would you need before accepting the newer result?