In aseptic processing, integrity testing is a critical step to ensure the performance of sterilizing-grade filters. But when exactly should integrity testing be performed? This article explores the optimal timing for pre-use and post-use integrity testing, and analyzes the regulatory requirements across different regions along with the underlying risk considerations.
When Should Integrity Testing Be Performed?
• Post-use: Testing should be conducted immediately after use.
• Pre-use: The decision should be based on risk assessment and regional regulatory requirements.
Let’s first examine the regulatory requirements for integrity testing in different regions and the objectives of testing at various stages.
1. Post-Use Integrity Testing
From both regulatory and testing objective perspectives, post-use testing requirements are highly consistent: as a vital step in ensuring sterility assurance for sterilizing filtration, integrity testing must be performed immediately after the filter is used.
Additionally, in-line testing should be employed whenever possible to better assess the integrity of the entire filtration system. If in-line testing is not feasible due to operational constraints, the filter should remain in its housing and be tested as an assembled unit, rather than being removed and tested individually.
2. Pre-Use Integrity Testing
Pre-use testing involves two stages: pre-sterilization and post-sterilization.
Both China and the United States require users to determine the necessity of testing at these two stages based on scientific risk assessment. In contrast, the European Union mandates that integrity testing must be performed post-sterilization and pre-use.
A Note on the Word “Should”
• US FDA Guidance for Industry: Process Validation: General Principles and Practices (2011) states: “The use of the word should in Agency guidances means that something is suggested or recommended, but not required.”
• PIC/S Recommendation on the Validation of Aseptic Processes (2011) states: “The term ‘should’ indicates requirements that are expected to apply unless shown to be inapplicable or replaced by an alternative demonstrated to provide at least an equivalent level of quality assurance.”
So, why do regulatory requirements differ across regions?
These differing requirements reflect distinct risk considerations.
Industry professionals supporting FDA regulations generally believe that if a filter has a defect, post-use integrity testing can still detect it. The consequence would be a delay in product release, causing economic loss to the company, but it would not allow a risky product to reach the market and create safety hazards. Therefore, the decision should be left to the manufacturer based on risk assessment.
Conversely, those supporting EMA regulations argue that filters can become gradually clogged during the filtration process. Very small defects might be masked by this clogging, leading to a “false pass” in post-use integrity testing. Such defects, however, can be detected in pre-use testing. Furthermore, since the sterilization process is the most likely cause of filter damage, pre-use testing should be conducted post-sterilization. Because the phrase “post-sterilization pre-use testing” is cumbersome, EMA coined the term PUPSIT (Pre-Use Post-Sterilization Integrity Testing).
The rationale and necessity of PUPSIT have been debated within the industry for nearly two decades.
1. Conducting testing post-sterilization is operationally complex and may increase the risk of microbial contamination.
2. The scenario where a micro-defect in a filter is masked by clogging during filtration, rendering it undetectable in post-use testing, has rarely, if ever, occurred.
In summary, integrity testing for sterilizing-grade filters should be performed immediately after use, preferably via in-line testing. For pre-use testing, the decision should be based on risk assessment and regional regulations: the EU and PIC/S require post-sterilization pre-use testing, while most other regions recommend pre-use testing, with the final decision to be made by the user based on scientific risk assessment.