Out-of-specification (OOS) result

A test result that falls outside the specification. Japanese documents also write it as OOS or simply as 'out of specification' (規格外). The investigation first asks whether the cause lies in the laboratory, such as an analyst or instrument error, or in manufacturing, and only a demonstrated laboratory error justifies invalidating the result. PMDA's ORANGE Letters, its anonymized notes on GMP inspection findings, have covered OOS handling. One from March 2025 described a site whose stability potency results fell below the approved lower limit on retest and which decided no action was needed, citing assay variability. PMDA called that inappropriate unless the OOS and the change over time could be ruled out with evidence.