Sterility Test Out of Specification (OOS): Causes, Investigation, and Regulatory Guidance
Sterility testing is one of the most critical quality control processes in the pharmaceutical and biotechnology industries. It ensures that sterile products — such as injectables, ophthalmic preparations, and implantable medical devices — are free from viable microorganisms. However, when a sterility test yields a positive microbial growth result, it is considered a Sterility Test Out of Specification (OOS) . Handling such an event requires a detailed, scientific, and compliant investigation process to determine the root cause and ensure patient safety. What is Sterility Test Out of Specification (OOS)? An Out of Specification (OOS) result in a sterility test indicates that the test outcome deviates from the established acceptance criteria — typically, the presence of microbial growth in one or more test units. Such a finding does not automatically confirm product contamination; rather, it triggers a comprehensive OOS investigation to determine whether the contamination or...