Sterilization Monitoring: Physical, Chemical and Biological Indicators
Updated October 27, 2026
A sterilizer cycle can’t be judged by looking at the packs. Sterile processing departments use three kinds of monitoring to show that each cycle met its conditions. This is a core part of the Sterilization Process on the CRCST exam. Here’s what to know, followed by free practice questions. Follow AAMI standards, the indicator and sterilizer manufacturers’ instructions, and your department’s policies.
Three kinds of monitoring
| Type | What it shows |
|---|---|
| Physical (mechanical) | The sterilizer’s own records of time, temperature and pressure for each cycle; review them at the end of every cycle |
| Chemical indicators (CIs) | A color or other change when exposed to certain sterilization conditions; used outside and inside packs |
| Biological indicators (BIs) | Living, highly resistant bacterial spores; if they’re killed, the cycle was lethal. The most direct test of sterilization |
Chemical indicator types
Chemical indicators are grouped into types (ISO 11140-1):
| Type | Use |
|---|---|
| 1 | Process indicators, such as indicator tape on the outside of packs, which show an item has been through a cycle |
| 2 | Specific tests, such as the Bowie-Dick test |
| 3 | Single-variable indicators |
| 4 | Multi-variable indicators |
| 5 | Integrating indicators |
| 6 | Emulating indicators |
A Type 1 indicator only shows that a pack was exposed to a process. It doesn’t show the pack is sterile.
Bowie-Dick test
Used in dynamic air removal (prevacuum) steam sterilizers to check that air is removed properly. It’s typically run each day the sterilizer is used, in an empty chamber, before the first processed load.
Biological indicators
- Steam and hydrogen peroxide BIs commonly use Geobacillus stearothermophilus spores.
- Ethylene oxide BIs commonly use Bacillus atrophaeus spores.
- Loads containing implants are monitored with a BI and should be quarantined until the BI result is known, except in documented emergencies, following AAMI ST79 and your policy.
Free practice questions
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Which type of monitoring gives the most direct evidence that a cycle killed microorganisms?Answer: BBiological indicators contain highly resistant living spores. If they're killed, the cycle was lethal, which makes BIs the most direct test of sterilization.
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What does indicator tape on the outside of a pack show?Answer: AExternal indicator tape (a Type 1 process indicator) only shows the pack went through a process, so processed and unprocessed items aren't mixed up. It doesn't prove sterility.
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In which sterilizers is the Bowie-Dick test used?Answer: CThe Bowie-Dick test checks air removal in dynamic air removal steam sterilizers, typically each day before the first load.
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Which organism is commonly used in biological indicators for steam sterilization?Answer: DSteam (and hydrogen peroxide) BIs commonly use Geobacillus stearothermophilus spores, which are highly resistant to these processes. Ethylene oxide BIs commonly use Bacillus atrophaeus.
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A load contains an implant. When should the implant be released for use?Answer: AImplant loads are monitored with a BI and quarantined until the result is known, because an implant stays in the patient. Emergency releases must be documented as the policy requires.
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What should be reviewed at the end of every sterilizer cycle?Answer: DReviewing the sterilizer's printout or electronic record confirms the cycle reached the required parameters before the load is released.
Pass the CRCST exam on your first try
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