Free tool · CRCST exam topic
Sterilization indicators
Choose what you need to prove — that a package was processed, that air was removed, or that the load was sterilized — and see which indicator does it.
Use
External chemical indicator (Type 1)
Indicator tape or the printed indicator on a pouch or label. It shows exposure to the process, not that the contents are sterile.
When
CDC: on the outside of each pack.
Use
Internal chemical indicator (Types 3–6)
Placed inside the pack or tray, in the area hardest for the sterilant to reach. Checked by the user when the package is opened.
When
CDC: preferably inside every pack.
Use
Bowie-Dick type air-removal test (Type 2)
Run in an empty chamber. Uniform color change across the sheet means air was removed; a pale spot shows trapped air.
When
CDC: daily, in an empty dynamic-air-removal sterilizer.
Use
Biological indicator (BI)
Spores of a highly resistant organism, usually in a process challenge device. The only monitor that directly measures lethality.
When
CDC: at least weekly for steam and low-temperature sterilizers, daily if used frequently, and in every load containing implants.
Use
Mechanical (physical) monitoring
The time, temperature and pressure recorded by the sterilizer’s gauges, display or printout, reviewed and signed for each cycle.
When
Every cycle.
Chemical indicator types 1–6
ISO 11140-1 (adopted in the US as ANSI/AAMI/ISO 11140-1) sorts chemical indicators into six types by intended use. The numbers are not a ranking: each type answers a different question.
| Type | Name | What it shows | Example |
|---|---|---|---|
| Type 1 | Process indicator | The package went through a sterilization process. Separates processed from unprocessed items. | Indicator tape, indicator on peel pouches and labels |
| Type 2 | Specific-use indicator | Designed for a specific test procedure, such as air removal. | Bowie-Dick type test sheet or pack |
| Type 3 | Single-variable indicator | Reacts to one critical variable of the cycle, such as temperature. | Temperature-only indicator |
| Type 4 | Multivariable indicator | Reacts to two or more critical variables. | Internal indicator strip reacting to time and temperature |
| Type 5 | Integrating indicator (integrator) | Reacts to all critical variables; its performance is correlated with a biological indicator. | Steam integrator strip |
| Type 6 | Emulating indicator | Reacts to all critical variables of one specified cycle (for example 132°C for 4 minutes). | Cycle verification indicator |
What CDC recommends for monitoring
- Mechanical: check the time, temperature and pressure for every cycle.
- Chemical: an indicator on the outside of each pack to show it was processed and, preferably, one inside each pack to verify sterilant penetration.
- Bowie-Dick test: daily, in an empty dynamic-air-removal sterilizer.
- Biological: at least weekly for steam and low-temperature sterilizers, with daily use allowing earlier discovery of problems when a sterilizer runs several loads a day. Each load containing implantable objects should be monitored.
- Positive BI: assume a sterilizer malfunction; items processed in that sterilizer are considered nonsterile, retrieved if possible and reprocessed.
Indicators on the CRCST exam
HSPA’s content outline lists the class or type and use of chemical indicators under Preparation and Packaging (placement and intended cycle), and monitoring under Sterilization Process. Expect questions on where each indicator goes, what a result means, and what to do when one fails. For cycle parameters, see the steam sterilization cycle times.
Test yourself: a CRCST-style question
Which monitoring method is the only one that directly shows a sterilization process was able to kill microorganisms?
- External chemical indicator
- Bowie-Dick test
- Biological indicator
- Sterilizer printout
Show answer
C. Biological indicator
Biological indicators contain highly resistant bacterial spores, so a negative result shows the cycle was lethal. Chemical indicators and mechanical printouts show that conditions were met; the Bowie-Dick test checks air removal.
Questions like this come up in the Sterilization Process section of the CRCST exam. The 901 questions in the app each come with a written explanation.
FAQ
- Is a Type 6 indicator better than a Type 1?
- No. The six ISO 11140-1 types describe different intended uses, not a ranking. A Type 1 process indicator and a Type 5 integrator answer different questions, which is why a package can carry both.
- Does a changed chemical indicator prove the item is sterile?
- No. Chemical indicators show that certain conditions were met at that spot. Sterility assurance comes from the combination of mechanical, chemical and biological monitoring, plus correct cleaning, packaging and loading.
- What happens if a biological indicator is positive?
- CDC’s guideline treats a positive spore test as a possible sterilizer malfunction: the sterilizer is checked, items processed in it since the last negative BI are considered nonsterile and retrieved if possible, and they are reprocessed. Follow your facility’s recall policy.
- How often is the Bowie-Dick test run?
- Daily, in an empty dynamic-air-removal (prevacuum) sterilizer, per CDC. Gravity displacement sterilizers do not use it because they do not remove air with a vacuum.
Sources
- CDC. Guideline for Disinfection and Sterilization in Healthcare Facilities (2008): Sterilizing Practices
- ISO 11140-1:2014. Sterilization of health care products — Chemical indicators — Part 1: General requirements
- HSPA. CRCST Exam Content Outline (revised November 2023)
Checked against CDC on November 13, 2026. For CRCST exam study only. Follow the indicator and sterilizer manufacturers’ instructions for use, ANSI/AAMI ST79 and your facility’s policy for placement, frequency and recalls.