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A helix test is a process challenge device (PCD) used to check whether steam reaches the inside of narrow, hollow instrument channels during a steam sterilization cycle. It is a coiled, narrow-bore tube with a chemical indicator at its closed end, and it is run inside the real load. It answers a different question from the Bowie-Dick test, which checks air removal in an empty chamber, and from a biological indicator, which uses spores. None of the three proves that every item in a load is sterile.
General information for lab and clinic staff, not medical advice. Follow your sterilizer manufacturer’s instructions and your facility’s written procedures.
Definition and scope
The CDC’s glossary for its Disinfection and Sterilization Guideline defines a process challenge device as an “item designed to simulate product to be sterilized and to constitute a defined challenge to the sterilization process” (CDC, checked 2026-10-30). A helix test is one such device, built for hollow loads. Tuttnauer, an autoclave manufacturer, describes its helix as designed “to verify steam penetration into narrow hollow instrument lumens” (Tuttnauer knowledge center, checked 2026-10-30).
One point is easy to miss: the CDC glossary has no entry for “helix” or “lumen” and its Sterilizing Practices page does not mention either. The helix test as described here is a manufacturer practice that Tuttnauer ties to EN 13060, the European standard for small steam sterilizers. It is not a CDC-defined test, so the CDC pages are cited below only for the tests and caveats they actually describe.
How a helix test is used in practice
According to Tuttnauer, the helix is placed in the actual load at the most challenging position, typically the centre of a densely packed tray, and it runs with the load rather than in an empty chamber. A biological indicator containing Geobacillus stearothermophilus spores can be added as an option, especially during validation. A complete, uniform colour change of the chemical indicator, and no growth from the biological indicator if one is used, is read by Tuttnauer as adequate steam penetration.
For frequency, Tuttnauer states “Daily for any Class B autoclave used to process hollow instruments,” and also describes use during operational and performance qualification when hollow loads are part of the validated family. That frequency is the manufacturer’s statement, not a CDC requirement. Your sterilizer’s instructions for use and your quality system set the schedule that applies to you. For how Class B and Class N machines differ, see Class B vs Class N autoclaves.
Helix test vs Bowie-Dick test vs biological indicator
The table maps each test to the question it answers. Every cell comes from the CDC glossary, the CDC Sterilizing Practices page, or Tuttnauer, as marked.
| Test | Question it answers | Where it runs | Frequency stated by the source | Source |
|---|---|---|---|---|
| Bowie-Dick test | Can the prevacuum steam sterilizer remove air from the chamber? | Empty dynamic-air-removal sterilizer | Daily (“must be performed daily”) | CDC |
| Helix test (PCD) | Does steam penetrate narrow hollow channels? | Inside the load, at the hardest position | Daily for Class B autoclaves used to process hollow instruments | Tuttnauer |
| Biological indicator | Does a commercial spore preparation survive the cycle? | In a test pack placed “in the area least favorable to sterilization” | At least weekly; each load containing implantable objects | CDC |
| Chemical indicator inside a pack | Did sterilant reach the inside of that pack? | Inside each pack, preferably | Each pack | CDC |
The CDC defines the Bowie-Dick test as a “diagnostic test of a sterilizer’s ability to remove air from the chamber of a prevacuum steam sterilizer.” The same page says a biological indicator test pack should “create a significant challenge to air removal and sterilant penetration.”
Where it matters for labs and clinics
Records that list “indicator passed” without saying which indicator are hard to interpret. A short checklist maps each question to the evidence that answers it:
- Is the sterilizer removing air? The daily empty-chamber air-removal test (CDC).
- Is steam reaching hollow instrument channels in this load? A helix-type PCD in the load (Tuttnauer).
- Did sterilant reach the inside of this pack? A chemical indicator inside the pack (CDC).
- Is the process killing spores? A biological indicator, at least weekly, and with every load containing implantable objects (CDC). The CDC adds that daily use of biological indicators “allows earlier discovery of equipment malfunctions.”
Tuttnauer lists the helix’s limits: it speaks for the load it travelled in, not the whole chamber; it describes Type 5 or 6 indicators as more informative than Type 2 for hollow loads; a passing helix does not replace the daily Bowie-Dick; and a passing Bowie-Dick does not confirm that hollow instruments were sterilized. For the indicator classes, see chemical indicators for sterilization. For validation records, see autoclave validation with biological and chemical indicators. Cycle choice is covered in autoclave cycle types, and the basics in what an autoclave is.
Common misunderstandings
A passing helix proves the load is sterile
It does not. The CDC states that the “pass” response of a chemical indicator “does not prove the item accompanied by the indicator is necessarily sterile,” and that a negative biological indicator “does not prove that all items in the load are sterile.” The CDC also says chemical indicators should be used in conjunction with biological indicators.
The helix replaces the Bowie-Dick test
Per Tuttnauer, it does not. The two check different things, in different places: chamber air removal versus steam reaching a hollow channel within a load.
The CDC requires a helix test
The CDC pages cited below do not mention a helix. What they require is the daily air-removal test in dynamic-air-removal sterilizers and the biological and chemical indicator practices in the table above.
FAQ
What is a helix test?
A process challenge device with a coiled narrow-bore tube and a chemical indicator at the closed end, used to check steam penetration into hollow instrument lumens (Tuttnauer, checked 2026-10-30).
Is a helix test the same as sterilization monitoring?
No. It is one tool in sterilization monitoring. The wider set combines chemical and biological indicators, and the CDC says indicator results alone do not prove sterility.
How often is the Bowie-Dick test done?
The CDC says an air-removal test (Bowie-Dick) must be performed daily in an empty dynamic-air-removal sterilizer.
How often are biological indicators used?
The CDC says at least weekly, and with each load that contains implantable objects.
For the link between monitoring and sterility targets, see sterility assurance level (SAL).
Sources
- CDC, Disinfection and Sterilization Guideline, glossary: cdc.gov glossary (checked 2026-10-30).
- CDC, Disinfection and Sterilization Guideline, Sterilizing Practices: cdc.gov sterilizing practices (checked 2026-10-30).
- Tuttnauer, Helix test guide (manufacturer page; statements attributed to Tuttnauer): tuttnauer.com helix test guide (checked 2026-10-30).
