By Mary Ann Drosnock

On March 3, 2022, the new ANSI/AAMI Standard, ST91, was published. Although it was released in 2022, the official date is 2021, since that is when it was approved by the working group and the sterilization standards board. ST91 (2021) is officially entitled “Flexible and semi-rigid endoscope processing in health care facilities”, and is applicable to the processing of all types of flexible endoscopes in all healthcare settings. ST91 (2021) is a replacement for the original from 2015, not an amendment, as we saw with the updating of ST79 for steam sterilization practices. So, it will be necessary to order the new document.

As an overview, the improved guidance document ST91 addresses both concerns about the risk of infection and patient safety, as well as new technologies. The new ST91 focuses on instituting additional quality measures to improve patient safety related to endoscope processing. There are an innumerable number of changes in both recommendations and requirements found within the document. Many topics that were recommendations in the previous version have moved to requirements of the standards, and many new recommendations are made.

Within ST91 there are many critical areas of focus, including an emphasis on training, competency, and certification, as well as considerations for the design of the processing area, environmental, HVAC, and water quality monitoring that have been updated. Critically evaluate these new recommendations and identify areas of noncompliance in your facility. To create your cross-functional team, involve leadership, facilities, environmental cleaning, infection prevention, biomedical engineering, and other departments in your evaluation.

Additional important updates include the renaming of precleaning to Point of Use Treatment. This is now standardized to the terminology found in ST79. There is also now a recommendation to note the time when the point of use treatment is performed and convey that information to the processing staff so that they know whether or not to follow the delayed reprocessing procedure. We call this step “hand-off communication”. Follow the delayed reprocessing procedure if more than 60 minutes have elapsed before manual cleaning is initiated.

The process for Leak testing has been changed to 60 seconds of observation instead of 30 seconds to allow for a thorough evaluation of the endoscope for leaks. Also, there is now a recommendation to test the leak test units for pressure output every day the unit is used. Another important update is the new designation of “high-risk” endoscopes. The standard contains different guidance for processing high-risk versus non-high-risk endoscopes. Examples of high-risk endoscopes are duodenoscopes, bronchoscopes, ultrasound endoscopes, and ureteroscopes among others.


Cleaning verification testing intervals have changed. ST91 now requires cleaning verification on all high-risk endoscopes with each processing cycle and a statistically significant portion of non-high-risk endoscopes. The document provides guidance on how to determine that portion in an annex. There are also strengthened guidelines around enhanced visual inspection using lighted magnification to evaluate the condition of the endoscope after manual cleaning but before disinfection or sterilization. Borescope inspection continues to be recommended at a periodic interval determined by the facility.

Another important point is that manual disinfection (i.e., soaking in a basin of high-level disinfectant) is no longer recommended due to the variability/inconsistency of personnel responsible for the process. This could have wide implications in non-hospital-based settings where manual disinfection is still performed regularly. Take an inventory of all the places within your facility where endoscopes are being processed. Likely, some or many of them still perform manual soaking in high-level disinfectant (HLD).

Additionally, ST91 strengthened the wording around sterilization processes and reemphasizes the original Spaulding Classification System. It states that all endoscopes should be sterilized, but if not possible, then we resort to high-level disinfection. If sterilization is available at the facility and the scope is compatible with that method, it should be sterilized. Everyone should be striving for sterilization for all endoscopes. Remember that endoscopes used in a critical application, (i.e., those used in a sterile area of the body) must be sterilized.

All endoscopes are now required to be completely dried both externally and internally before reuse, even post-AER processing. And it does not matter whether the endoscope is going into the storage cabinet or back to immediate reuse, all scopes should be subjected to a compressed air-drying cycle of 10 minutes or placed into an active drying cabinet to dry internally. This will add time to the processing cycle.

These highlights are only a few changes worth mentioning in the new ST91. It is recommended that each facility obtain a copy of the new standard and begin a thorough review. Assemble a multi-disciplinary team to review the guidance and create a crosswalk of noncompliance topics based on the current practices at the facility. Create an implementation strategy with assigned due dates. That way facilities can prioritize issues and begin the implementation of the changes. This is an important update to the standard that will increase quality in endoscope processing and therefore patient safety.

The new standard is available at this link.

About the author: Mary Ann Drosnock is the director of clinical affairs at Healthmark Industries.