In this series of Q&A posts, we’re answering questions from customers about USP <797> compliance. Some of these are common questions. Others, not so much. All are important.
Today, I’d like to respond to a few questions about pass-through sampling that we received during and after our webinar on Personnel Competency and Environmental Monitoring. This webinar is now available on demand.
Q: Can you clarify what a pass-through is?
We discussed pass-throughs at a high level in the webinar, so I’m happy someone reached out with this general question. It gives us a chance to clarify the issue for a broader audience. It also shows others that they aren’t alone if they still have what seem like very basic questions.
While the USP <797> standard does not explicitly define a pass-through, it is generally understood to be a space designed to minimize contamination when transferring materials into and out of a cleanroom or sterile compounding area. For example, a pass-through chamber may be a hallway or small room connecting a chamber with a lower classification to one with a higher classification. In this example, the pass-through allows both people and product to pass from one chamber to another.
A pass-through may also be designed to transfer product from one chamber to another. For example, a transfer hatch allows personnel to minimize the possibility of contamination when passing product or components from one space to another. Enclosed carts may also serve the same purpose. CAIs and CACIs typically have pass-throughs on one or both sides.
Q: Is a pass-through considered a cleanroom?
Like the environments they protect, pass-throughs could be considered an ISO-classified space. Air quality requirements of the pass-through units should be defined by the engineering controls of the connected spaces. Industry best-practice is to assign the ISO classification of the cleaner of the spaces connected by the pass-through chamber or transfer area. So, if the pass-through goes from an ISO 8 to an ISO 7 area, you would assign the ISO 7 classification to the pass-through.
Q: Is Sampling Required for Pass-Throughs?
What you’re compounding in the connected chamber(s) determines how often sampling is required. Per the standard, Category 1 and Category 2 CSPs (low and medium risk) require surface sampling of all classified areas, including pass-through chambers, at least monthly. Category 3 CSPs (high risk) require weekly surface sampling and sampling at the end of each batch. To be clear, even though compounding is not being conducted in the pass-through chamber, surface sampling is required at the same frequency as the sampling required in the higher of the connected ISO-classified areas.
Q: Is surface sampling only required if the pass-through is a non-ISO classified area and not HEPA filtered?
We answered this in the last question, but it’s worth repeating, as it represents a change from the previous version of the standard. The 2022 USP <797> standard states that pass-throughs connected to an ISO-classified space must be tested, regardless of whether the other side of the pass-through is non-ISO classified. Likewise, HEPA filtration is not a factor so far as sampling requirements are concerned, although it can be a factor in the ISO classification of the pass-through.
Minimum Standards
In some ways, the 2022 revisions tightened up the USP <797> standard, e.g., requiring pass-through surface sampling. However, they also leave some details, such as pass-through cleanroom classification, up for interpretation. I’ll close by re-emphasizing what you hear me say so often. The revised USP <797> standards serve as a minimum. When in doubt, following industry best-practices can help. However, the onus is on your organization to ensure the safety and efficacy of your compounded sterile preparations (CSPs). You should be customizing your Standard Operating Procedures (SOPs) based on your initial risk assessment and revise them as necessary based on sampling results.