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Performance Qualification (PQ): The Proof

This is the final article on the subject of process equipment qualification. As a reminder, we qualify process equipment to ensure:

  • The equipment is what was ordered
  • The utilities are sufficient
  • The cycles run as expected
  • The cycles run really do what you need them to do

This last point is the subject of this article, performance qualification. As you may recall, in the first of these articles, I provided the following definition of the array of testing and my interpretation of it:

Let’s look at the critical pieces here.

Do what you expect
It washes, it sterilizes, it dries, it checks insulation integrity, it illuminates, it images the interior of a lumen, etc.

Reliably and repeatedly
It does the same work every time. If it doesn’t do the job reliably and repeatedly, it isn’t worth having.

Obtaining and documenting evidence
You run test cycles or operations that challenge the limits of performance of the machine or device being qualified.

In an industrial or manufacturing setting, the challenges are extreme, with, for example, sterilization run in a half cycle (half the duration of the exposure stage instead of the full duration). In a sterile processing department, extreme measures are less needed, since many of the items you are testing have been validated for performance in getting their FDA clearance. If the device does not require FDA clearance (washer-disinfectors without high-level disinfection claims, for example), there is still oversight of the manufacturer since they sell into the healthcare market.

So, how do we do this? For steam sterilizers you simply follow ANSI/AAMI ST79:2017, section 13.8, “Qualification testing,” and monitor the postvacuum/drying behavior to make sure that the temperature goes down first (wet load) and then increases to about 180+°F (dry load). If this isn’t the case, you either have wet steam or anemic vacuum performance due to the temperature of the water fed to the pump or ejector being too warm. And you have your steam supply to the sterilizer tested to show dryness, superheat, and noncondensable gas compliance with ST79 section 3.3.3.

For vapor hydrogen peroxide sterilizers, take a similar approach using process appropriate PCDs. Before someone asks about hydrogen peroxide plasma sterilizers, remember, “plasma” is only used to reduce hydrogen peroxide residuals and has nothing to do with the sterilization process.

For washer-disinfectors and ultrasonic cleaners, section 13.2 is a start on this, with Annex D expanding on it. The issue with washers is to adequately challenge the process. There are no standards for cleaning indicators, and if you have ever compared the cleaning results of the indicators available on the market, you would know that their resistance to the washing process is not the same from manufacturer to manufacturer. Since washer parameters are not set in stone as those for sterilizers are (for most washers), you can tweak (optimize) washer cycles to improve performance to where cleaning is always going to be successful if the cycle runs correctly. If you have lumen connections on racks or in a sonic, those have to be tested as well. A number of manufacturers have lumen adapters for cleaning indicators.

It is suggested that you compare indicators, choose the most difficult one that can provide a lumen test, test and optimize cycles, then do your PQ. You can also apply commercially available test soil to test objects and measure for residual markers (protein, ATP, carbohydrate, etc.). This needs to be done before and after washing to ensure the residuals are detectable by the chosen method unless the manufacturer of the test has identified the markers as being detectable by their detection method. The current limits for detection from ANSI/AAMI ST98 (in preparation) are:

  • Protein ≤ 6.4 μg/cm2
  • Carbohydrate ≤ 1.8 μg/cm2
  • Hemoglobin ≤ 2.2 μg/cm2
  • Adenosine triphosphate (ATP) ≤ 22 femtomoles/cm2

If your results are near these or lower, you are in good shape for process qualification. Note that these should be tested with no thermal disinfection phase, since that can denature the marker, giving you a false negative result.

Cycle optimization may cause cycles to run a little longer, maybe even an additional 10 minutes. I know everyone wants washer cycles that take exactly 10 seconds or less, but let’s look at the impact of a 10-minute increase on productivity and how it compares to other process situations in the SPD. If you are having to crack the door of a steam sterilizer to let the load dry before removal, you have problems with the sterilizer. Either the steam is wet, the sterilizer is misloaded or overloaded, or the drying vacuum is not effective enough (see above). Proper PQ of the sterilizer would solve these issues, so there’s 10 minutes to a half hour that you just got back that you can use to ensure proper cleaning of the instruments.

Similar approaches can be taken for any item that is critical to processing success.

How many times do you have to test each cycle or configuration (lumen rack, etc.)? Three successive compliant cycles. Compliant means that the cleaning results were as desired; successive means three in a row.

Why do you do this? So you will know that the expensive equipment you bought with your facility’s hard-earned money (that you had to beg for and sweat blood to get) actually works, and, most important, when properly maintained, will always be able to perform at this level over the course of its use life. Because IQ, OQ, PQ are just the beginning of ensuring quality performance of processing equipment. Requalification should be an annual event. It consists of a repeat of the PQ, as long as no major changes have happened. Why do this annually? To have documented proof that your equipment is in the best state it can be. And to maintain patient safety. And to impress the accreditation agencies.


Dr. Jonathan Wilder has worked with all thermal and chemical sterilization methods, as well as cleaning and disinfection methodologies, bringing his background in physical chemistry and surface physics to bear upon difficult problems in the field. He has been an active participant in U.S. and international standards development since 1998 through AAMI. As of January 2018, he is the cochair of the U.S. standards-making committee for hospital steam sterilizers.

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