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Cleaning Indicators: What, Exactly, Are They Telling Us about Washer-Disinfectors?
By Jonathan A. Wilder, Ph.D., Managing Director

Do you test your washers? AAMI ST79:2017, section 13.2, says, “Mechanical cleaning equipment should be tested upon installation, each day that it is used, and after major repairs.”(I would add that full testing should be done when a new detergent is put into use. They are not all the same.) Okay, now that we’ve determined that you should be testing, what, where, and how should you be testing? And what do the results tell you?

Routine testing
Many SPD managers have chosen to test daily with a less expensive indicator that is thought to be easier to clean, and test weekly with a more expensive indicator that is thought to be harder to clean. This allows you to challenge the washers, meet the letter of the law of ST79’s requirement while keeping the budget under control, and (optionally) test more locations using the less expensive indicator. In either case, you are challenging the washer and ensuring that it is working to some measurable, repeatable level.

This is a good approach. It saves money and still lets you keep the finger on the pulse (or, if the daily test fails, arrhythmia) of the washers.

Which indicator is more resistant?
Which indicator is harder to clean and which isn’t? There are no standards for cleaning indicators at this time. This is more than a bit different than sterilization indicators where all have more or less the same resistance to the process, and if they don’t, the D-value and population tell you how much different their resistance is. But that is the subject of another article. Because the financial side is easy (you just look at the price), how do you figure out which is more resistant to the washer process? Test. I will provide a testing procedure at the end of the article that lets you compare. No matter what your results are, testing with any indicator is far better than not testing.

Where should I put the indicator(s)?
In the most challenging location in the washer. Where is that? There is no general answer to that question. Every installation is different and each washer in each installation is different, too. What do you do to figure this out? Test again using the same procedure at the end of the article.

This test tells you where the process challenge location (PCL) is. Once you know this, you can test there and only there with reasonable assurance that the rest of the washer chamber is cleaner. Note that different washer trolleys may have different cleaning characteristics. Each type of trolley should be tested individually and the PCL noted so you will be able to test at that location on a daily basis.

Which indicators do I use and when?
The challenge each indicator provides to the wash process is similar from indicator to indicator of the same product, but can be different from manufacturer to manufacturer and product to product. Also, the process challenge device offered with some cleaning indicators can make a large or small difference in the cleaning performance shown by the indicator.

For weekly challenges, PCL determination or its reverification, you want to use the most difficult-to-clean indicators you can find and you want to use an abbreviated cycle. Why? A clean indicator tells no tales. An abbreviated cycle will make it more likely that the indicators are not completely clean. Of course, if the indicators show no cleaning, you have a different issue and may want to talk to the manufacturer of the washer or detergent, or a consultant to carry out process optimization.

Most difficult-to-clean indicators may not come completely clean, even in an optimized cycle. If they are consistently not clean in the same location in the washer, and if the amount of remaining soil or equivalent is the same each time, you can document that photographically and use that as a baseline for the expected capability of the washer.

For daily testing, any cleaning indicator may be used at the PCL, as long as you use the same indicator brand and model. If a process challenge device (PCD) is used, always use it; if not, never use it. Daily testing serves to point out gross problems in the washer’s function. Weekly testing with a difficult-to-clean indicator serves to verify proper function and, if performance is seen to degrade over time, shows an early indication of problems that an indicator which is completely cleaned might not detect until a major process failure is at hand.

If I can’t see soil, is it clean?
Maybe. You can’t see many proteins on a metal surface. For blood- and protein-based indicators, you can do a test for invisible, residual protein. Some indicator manufacturers provide you a means of testing the residual protein level. Others that do not can be analyzed by sampling using a protein test swab.

What are the indicators telling us?
There are two answers: a lot and not as much as we’d like. Systematic testing of your washers gives you a safety net. Daily testing at a PCL that you have located by testing tells you that you don’t have a catastrophic failure. Weekly challenge testing shows you trends in the washer’s performance and gives you a heads-up of any washer issues that may be developing. These tests, while effective and repeatable, are limited in that they don’t easily tell you if all of the soil on every instrument is being removed. They are a major step up in assuring good cleaning, but they are only part of the process of cleaning. Staff training, instrument design, washer design and maintenance, and cleaning chemistry are all critical parts of creating good outcomes.

Testing procedure for washer and indicator evaluation
Test how, you say? There is a procedure in the German Guidelines for Washer-Disinfector Validation2
that is informative. In the course of required, onsite revalidation of the washer (required in Germany, not in the U.S.), you place two indicators on diagonally opposite corners of the top shelf of the washer-disinfector. Then you place three indicators on any intermediate level: one in the middle, and two at 12 and 6 o’clock positions. Finally, on the bottom level, place two indicators at the diagonally opposite corners. Testing per the guideline is done with a normal washer load.

To determine the location of the least cleaning capability or, in standards-speak, the PCL, you should do in-depth testing like this after installation, major repair, and annually (since the location may change as the washer ages), or to evaluate indicator resistance and detergent efficacy. This testing is done for three cycles to ensure that average results are determined and not outliers. Testing like this shows you where the washer does not clean as well and allows you to systematically test indicators for comparative resistance to help you choose your test products. But you don’t have to test in this depth every day. This is the beginning. Testing that assures that the entire washer chamber is cleaned is the result.

References

  1. AAMI ST79:2017, 13.2
  2. “Guideline compiled by the DGKH, DGSV, and AKI for the validation and routine monitoring of automated cleaning and thermal disinfection processes for medical devices” 5th Edition 2017; German Society for Hospital Infection Control (DGKH), German Society for Sterile Processing (DGSV), and Working Group for Instrument Processing (AKI); Zentral Sterilisation, Supplement  2017; mhp Verlag, Heidelberg, Germany, copy available on request.

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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