“How do you know it’s sterile?” is a question commonly asked in Central Sterile Processing. Thankfully, our technicians have multiple methods and tools at their disposal to prove the completion of the sterilization cycle. The answers that these tools give CSP professionals are called “Sterility Assurance Levels” or SALs. When first entering a Central Sterile Processing Department (CSPD), you might find it difficult to comprehend the technical aspects pertaining to how SALs equal sterility for the end users. AAMI ST79:2017 2022 quotes SAL as the “Probability of a single viable microorganism occurring on an item after sterilization. SAL is normally expressed as 10n. A SAL of 106 means that there is less than or equal to one chance in a million that a single viable microorganism is present on a sterilized item” (AAMI, 2022). This is how the CSPD shows that the instruments are processed adequately and are safe for patient use, and this is where indicators come into play.
There are two common types of indicators used in CSP, and they each have sub-qualities important to the sterilization process. There are chemical indicators, which are placed with the items being sterilized to show the end users that the instruments have been exposed to the sterilization process. Then there are biological indicators, which are used by CSP to confirm that the sterilization machines have performed their cycles perfectly.
Chemical Indicators
Chemical indicators (CIs) confirm that sterilization practices have been performed by changing colors in various ways depending on how they’re made. These range from type 1-6. ANSI/AAMI is the American National Standards Institute, and AAMI is the Association for Advancement of Medical Instrumentation. Together, they standardize practices through a census of experts ranging from regulatory agency representatives and manufacturers to end users and subject matter experts. These bodies meet to discuss best practices backed by scientific data and create standards such as ST58 and ST79, as well as technical information reports such as TIR109. Based on ANSI/AAMI standards, chemical indicators are divided in the following manner.
Type 1: Process indicator. A process indicator shows the package has been exposed to a sterilization process. This could be locks with indicator dots, external indicator tags, or sterilization tape. Once sterilized, the indicator portion will change colors to show that the item has run through the process, but not necessarily that it has reached a 10-log-6 level of organism reduction.
Type 2: Specific test indicator. A specific test indicator shows the results of one particular sterilization modality. This includes the Bowie Dick, also known as the Dynamic Air Removal Test (DART test). The DART test is specially made to prove that enough air is removed in the pre-vacuum stage of sterilization so that the steam pulse can penetrate the filters or wraps as well as enter lumened items inside the tray. DART tests should be run each day when the sterilizer is in use.
Type 3: Single critical process variable indicator. These react to a single parameter, such as temperature. Single variable indicators react at a specific stated value, but that is the end of their limitation, and so they are rarely used in our industry.
Type 4: Multicritical process variable indicators. These are similar to type 3 but react to two or more variables at stated values. This could include time and temperature. These are not typically used in CSP because they do not react to all critical parameters.
Type 5: Integrated indicators. Also known as integrators, these react to all critical parameters of the sterilization process, which are exposure time, temperature, and pressure. They are placed within the package to be verified in the sterile field. Type 5 indicators meet or exceed the 11138 series of biological indicators. The 11138 series of biological indicators are standardized tests with specific microorganisms that are known for their resistance to sterilization. These indicators are used to ensure that sterilization methods are effective in healthcare, pharmaceutical, and laboratory settings and validated by the International Standards Organization (ISO). These interrogators are placed inside the sterile packaging to show that the sterilant has penetrated the tray and the instruments have been exposed to all of the correct sterilization parameters. These will change color when the minimum parameter requirements have been met.
Type 6: Emulating indicators. These indicators react to all critical parameters of sterilization, but only for a specific sterilization process. These indicators will not change if exposed to improper sterilization parameters.
Of the CIs, types 1, 2, and 5 are the most used of these types of indicators.
Biological Indicators
Biological indicators (BIs) are live spores enclosed in a protective device designed for contained incubation. These spores, such as Geobacillus Stearothermophilus or Bacillus Atrophaeus, are resistant to specific modalities of sterilant, so proving that they can be eradicated helps CSPD technicians attest that the instruments are safe for use.
A BI and a type 5 chemical indicator, packaged in a Process Challenge Device (PCD), are only required to be run at specific moments in the instrument workflow cycle. These times are during sterilizer testing after major repairs, with implantable surgical items, or at a minimum of weekly; it is preferred by AAMI to be run daily. Many healthcare facilities choose to run a BI and indicator on every sterilization load. When a BI fails the incubation test, all of the instruments run in that cycle must be recalled to CSP and reprocessed.
If only one PCD is run per week, then there are potentially hundreds or thousands of instruments that must be recalled or have already been used on a patient. Testing for every cycle means only one sterilizer load would need to be recalled for reprocessing. A BI is considered to “pass” when, after being incubated for the indicated amount of time, the spore is “negative,” meaning that it has effectively been killed by the sterilization cycle. If a BI fails, it will read as “positive,” meaning positive for microbial growth. To ensure that the BI lot number isn’t faulty, the biological indicator should have a control run every 24 hours or with every lot change. A control is a BI that has not been processed in a sterilizer. This means that it should read as “positive” or a failure, and that the lot has viable spores prior to the sterilization process.
Along with the BIs, physical indicators or mechanical indicators are typically only seen by CSPD technicians unless otherwise requested by other departments or individuals. These physical indicators include sterilizer printouts, charts, digital sterilization records, and parameter screens. These records show a plethora of information such as load counts, sterilizer information, exposure times, temperatures, and pressures within the chamber. Technicians should be fluent in their ability to read these records to visually verify that the sterilizer sensors' recorded information matches known parameters for the selected cycle.
Lastly, there are administrative or process indicators. These include load stickers, sterilization logs, package labeling, and testing logs. These are indicators created by CSP to track all of the sterilization information for every instrument that is run through the sterilizers. This includes information on the technician who assembled the instruments, what sterilizer and load number the instruments were processed in, and more information.
When all of these are used together, a competent technician can show that the sterilizer is operating correctly, who assembled the set, how it was processed, that the process sterilized the set to the correct parameters, and the set has not been tampered with post-sterilization. Indicators are small but vital tools in the sterilization cycle. If an instrument set is missing internal indicators (those Type 5s!), then the end user is supposed to reject the set. There is no physical evidence that the instrument went through the entire sterilization cycle. Indicators are required to prove process completion.
Next time you’re asked, “Did you remember the indicators?” you can reply with “Which ones do you want me to show you?” You have the knowledge to properly ensure that your fellow technicians, leadership, and end users know that your instruments have been sterilized and are ready for patient use.
About the Author
Nelson Winter
Nelson Winter III is a healthcare leader who is a lifelong learner who values the industry
and the community within it. His participation is exemplified in his participation in
the Keystone Alliance of Sterile Processing Professionals where he serves as Vice
President. He has multiple industry certifications and serves on the Beyond Clean Advisory
Group. Nelson is the primary voter for his system in the AAMI workgroups and has served
as a SME for the HSPA certification tests. He is currently pursuing his associate's degree
and implements his acquired knowledge and new technologies in his department to better
serve his patients.
Vanessa Frank
Vanessa Frank, Clinical Resource Manager at Advantage Support Services, Inc., leverages her expertise in sterile processing and healthcare management. As Chapter President for the Keystone Alliance of Sterile Processing Professionals, she advocates for best practices and ongoing professional development. Her career includes roles as a Sterile Processing Technician, Educator, Content Marketing Specialist at Censis Technologies, and CE Development Support at Beyond Clean. With over 13 years of experience, Vanessa specializes in quality management, SOP development, and training. She is pursuing a BBA in Health Care Administration/Management and holds several professional certifications, reflecting her commitment to advancing healthcare practices.