As you consider your options, it is important to clearly understand each device, its intended use, and potential limitations. Please take a few moments to review the performance questions and answers below.
What are the differences between Class 5 Integrating Indicators and Class 6 Emulating Indicators?
Biological Indicators:
Biological indicators are designed to demonstrate whether the conditions were adequate to achieve sterilization. Biological indicators contain a known number of resistant spore forming microorganisms to monitor adequacy of the sterilization process.
Because biological indicators are the only true measure of the sterilization process lethality, they are considered to be the highest level of sterilization cycle monitoring. BI's are widely recommended as the preferred monitoring device for releasing loads and monitoring sterilization cycles.
3M Comply™ SteriGage™ 1243 Chemical Integrator
Class 5 Integrating Indicators:
Class 5 integrating indicators are designed to react to all critical variables (time, temperature, and the presence of steam) and have Stated Values that correlate to a BI at three time/temperature
relationships.1
Class 5 integrating indicators must have three Stated Values at 121°C, 135°C, and at one temperature in between that correlate to a BI.1 Additionally, the Stated Value at 121°C must not be less than 16.5 minutes. This guarantees the time/ temperature response for a Class 5 integrating indicator will respond like a BI when exposed to ideal, saturated steam (see Figure 3). Therefore, if the exposure temperature was not achieved where the Class 5 CI is located and the BI result was positive (indicating a sterilization failure), the Class 5 CI will respond like the BI (thermal death rate curve of G. stearothermophilus) and also indicate that a failure had occurred.
Class 6 Emulating Indicators:
Class 6 emulating indicators are designed to react to all critical variables (time, temperature, and the presence of steam) for a specified sterilization cycle.1 You may hear Class 6 indicators referred to as cycle specific indicators.
Class 6 emulating indicators have one Stated Value for time and temperature for the specific cycle it is designed for.1 There is no requirement for three Stated Values for time and temperature and therefore the response may not correlate to a BI (see Figure 4) throughout the temperature range. Note that at lower temperatures the Class 6 response can fall below that of the BI performance (thermal death rate curve of G. stearothermophilus) (see Figure 4).
How does this effect my monitoring process:
Biological indicators continue to be the highest level of sterilization cycle monitoring and are widely recommended as the preferred monitoring device for releasing loads and monitoring sterilization cycles.
If your Sterile Processing Department runs multiple exposure times (e.g. 4, 10 and 18 minutes at 272°F), a distinct Class 6 emulating indicator would be required to monitor each cycle.
BI’s provide the only direct measure of sterilization process lethality. Chemical indicators and emulating indicators seek to mirror the death curve of a BI or response at a specific temperature, respectively.
How are BI’s and CI’s tested:
Class 5 integrating indicator and Class 6 emulating indicator performance is not tested in poor steam conditions such as superheat or air/steam mixtures. Additionally, CI performance compared to a BI is also not tested in these poor steam conditions. Because the Class 5 integrating indicator response at lower temperatures parallels the biological response, Class 5 CIs are able to detect the failure condition where the desired exposure temperature is not achieved. This condition is likely to occur when there is:
- incorrect packaging
- incorrect loading
- air/steam mixtures
- an incorrect cycle for load contents
Because the Class 6 response at lower temperatures can fall below the thermal death curve of G. stearothermophilus, the Class 6 emulating indicator can reveal a pass when the BI would indicate a failure.
1Association for the Advancement of Medical Instrumentation, Sterilization of health care products - Chemical indicators - Part 1: General requirements, ANSI/AAMI/ISO 11140-1:2005.
Has 3M completed performance testing of Biological Indicators, Class 5 Integrating indicators, and Class 6 Emulating indicators in failure conditions?
Yes, 3M has tested its biological indicators and Class 5 integrating indicator as well as two commercially available Class 6 emulating indicators in several different steam sterilization conditions. The data from these studies was used to generate the graphs in Figures 3 and 4. The tests were done in a steam resistometer, the special test vessel that generates ideal saturated steam and is the vessel required for ANSI/AAMI/ISO Compliance Testing. What this testing revealed is that the 3M Class 5 integrating indicators do, in fact, correlate to the biological response or thermal death rate curve of G. stearothermophilus. Even though the Stated Values of the Class 6 emulating indicators were 3.5 minutes at 134°C, their time/temperature response compared to the biological response was faster at lower temperatures.
This 3M study also included testing 15 of each type of Class 5 and Class 6 indicator in a shortened, hospital type cycle (see Figure 5). All the Class 6 products gave a PASS result which means they failed to detect the shortened exposure time even though their Stated Values at 134°C were greater than that of the Class 5 product. This data shows that the Class 6 products responded during the come-up time and progressed to their endpoint too soon to detect the steam sterilization process failure that occurred as a result of not remaining at the exposure temperature for an adequate time.
These monitoring products are tested under ideal saturated steam conditions to satisfy both FDA
guidance document and ISO performance testing requirements. However, a scientific study investigating performance of these monitoring products in suboptimal steam sterilization conditions, e.g. superheated steam and incomplete air removal, reveal that only biological indicators are capable of consistently detecting these types of failure modes.5 Thus, biological indicators will respond correctly by showing positive results under common failure modes, whereas chemical indicators may not.
5AJIC, Vol. 33, No 5, Supplement 2, June 2005 Performance of Various Steam Sterilization Indicators Under Optimum and Sub-Optimum Exposure Conditions.
Does the Class number have any significance? For example, is a Class 6 CI better than a Class 5, and do Biological Indicators have a class?
Today, there are six classes of chemical indicators. The current ISO document classifies chemical indicators by their intended use and these classifications have no hierarchical significance.1 For example, the Bowie-Dick Test is a Class 2 chemical indicator and probably provides more information about the steam sterilizer performance than any other class of chemical indicators. ISO provides performance requirements for each classification.
Biological indicators are not subject to a classification system. Biological indicators required for a sterilization process contain resistant spore-forming microorganisms to respond to the conditions within the cycle. Chemical indicators can be made with a multitude of different formats and chemistries. Thus, how they respond to the sterilization process can differ depending on the design. A process or single variable chemical indicator is only required to respond to one of the critical variables, while another type of indicator (ie. a Class 5 integrating indicator must respond to all of the critical variables).
1Association for the Advancement of Medical Instrumentation, Sterilization of health care products - Chemical indicators - Part 1: General requirements, ANSI/AAMI/ISO 11140-1:2005.
