The U.S. Food and Drug Administration (FDA) draft guidance document for the processing and reprocessing of medical devices has recommended that if a device is to have a life of 100 cycles of use and reprocessing, it needs to be validated to 100 cycles. Likewise, endoscopes and other medical devices need to be tested for a buildup of soil. Testing for these two different conditions is very similar, but looks for very different results.
 
Functionality testing looks at the use and reprocessing of the medical device. If a device is labeled for a life of 100 cycles, it should be tested to ensure the device is functional after 100 cycles. This test does not look at cleanliness, just that it is still functional after the stated number of use cycles by the medical device manufacturer.
 
On the other hand, simulated-use testing examines the soil buildup on a medical device to ensure it remains safe during the life of the medical device. This test focuses on cleanliness, and determines if there is buildup of soil and debris during the duration of the life of the device. Accumulative buildup on the device most likely makes the device unsafe by harboring organisms or releasing infection or toxins.
 
Both the functionality of the medical device and the ability to resist soil buildup has been a concern in the medical device industry. The need of the assessment for testing functionality and simulated use has been specified in the draft guidance document specified above.
 
Human factors may play a role in the consideration of end-of-life testing. For example, a medical device may have a stated end of life of 100 cycles, but most healthcare facilities do not have a way of tracking the number of times a reusable medical device is used. Often, the device is considered functional until a medical professional determines it no longer is—then a facility will retire the device.
 
Likewise, a medical device could begin to buildup soil to a level detrimental to patients’ health even though it may be deemed functional since the buildup may not be seen.
 
The question remains, at what point is the buildup is unsafe? The fear is that the buildup or debris could be toxic, harbor organisms, or prevent sterilization.  All of these issues deem the device unsafe. Simulated use testing answers that question and should be factored into the end-of-life cycles of the medical device by the device manufacturer.
 
The validation plan for both simulated use and functional testing is virtually the same. The medical device is soiled/contaminated with simulated use test soils, cleaned, and disinfected/sterilized for the appropriate number of cycles—at least up to the number of cycles recommended by the medical device manufacturer in the Instructions for Use (IFU).
 
It is preferred by the FDA, as well as recommended by Nelson Laboratories, that full life-cycle testing for functionality, which includes all the steps of the processing cycle, be performed and validataed.
 
Additionally, manual and automated cleaning needs to be factored into functionality testing. The automated usually is preferred compared with the manual cleaning for functionality tests because it may cause more wear on a device due to the high pressure washes and detergent concentrations that the medical device receives during the cycle. Medical device manufacturers need to validate to one cleaning method or the other, or to both, depending upon the medical device.
 
The most important aspects of functionality and simulated-use testing are to ensure that a medical device meets both the FDA guidance criteria and remains safe and functional, throughout the life of the device. A clear IFU will help ensure this safety, but it must be remembered that many medical facilities rely on the healthcare professional or surgeon to determine if the device is still functional.

About the Authors
• Emily Mitzel, M.S., B.S., is a laboratory manager at Nelson Laboratories in Salt Lake City, Utah. She is an expert in reusable device reprocessing validations, pharmaceutical testing and microbiology testing. She is a committee member with AAMI, ASTM and serves as co-chair for Working Group 95.

• Alpa Patel, B.S., R.M. (NRCM), is a certified microbiologist and a senior scientist at Nelson Laboratories. She specializes in cleaning/disinfection and sterilization of reusable medical devices. She is responsible for writing protocols for special projects.

• Nick Workman, CQPA (ASQ), is a study director III at Nelson and specializes in cleaning/disinfection and sterilization of reusable medical devices. He consults and guides clients through the FDA 510(k) submission process for reusable medical devices.