ISO 11138-5 Low-Temperature Steam Formaldehyde Indicators: A Canadian Buyer's Guide
A clinic that runs a low-temperature steam formaldehyde unit usually meets ISO 11138-5 the hard way: at the moment someone asks what the spore test result actually proves. The unit is doing real work on heat-sensitive instruments and the log looks full, but a reviewer asks whether the indicator was qualified for that cycle at all. A 24-hour self-contained biological indicator, 50-pack answers that question for a steam load, not for an LTSF load, and the difference is the point of the standard.
What does ISO 11138-5 cover?
ISO 11138-5:2017 sets requirements for test organisms, suspensions, inoculated carriers, biological indicators and test methods used to assess processes that employ low-temperature steam and formaldehyde as the sterilizing agent. It is the part of the 11138 series written for that chemistry, as ISO 11138-3 is the part written for moist heat. It defines what the indicator manufacturer had to test, and therefore what the certificate can honestly claim.
Can a steam spore test substitute for an LTSF indicator?
No, and the failure is quiet rather than loud. A steam indicator carries spores selected and tested for a moist-heat cycle; an LTSF cycle runs with formaldehyde below ambient pressure. Organism, carrier and resistance figures are established under different conditions, so a pass on the wrong product says nothing about the cycle you ran.
| Compare | Steam, ISO 11138-3 | LTSF, ISO 11138-5 |
|---|---|---|
| Cycle named | Moist heat at steam temperature | Low-temperature steam and formaldehyde |
| Test organism | Specified for moist heat | Specified for the LTSF process |
| Resistance data | D-value at labelled steam conditions | D-value at labelled LTSF conditions |
| Population | Spores per carrier | Spores per carrier |
Where does validation sit, ISO 25424 or ISO 14937?
This is the detail most buying guides skip. ISO 25424:2018 specifies requirements for development, validation and routine control of an LTSF process using a mixture of low temperature steam and formaldehyde below ambient pressure. The 2017 edition of ISO 11138-5, meanwhile, still refers readers to ISO 14937 for validation and control. The practical rule: cite ISO 25424 when your procedure describes how the process is validated, and ISO 11138-5 when it describes the spore test. Mixing the two in one sentence is how audits get interesting.
What should the purchase order state?
Put the standard and edition on the line item, not just the product name. Require the certificate to name the process, the test organism, the population and the D-value, and require each carton to carry a lot number and expiry that match it. Then check storage and incubation: an incubator set for one label is not automatically right for another.
For the steam side of the same clinic, a 1-hour fluorescence rapid readout biological indicator, 50-pack shortens release time, and a 4-well fluorescence biological indicator reader reads the result without a separate incubation step. Running a dental practice? Our dental practice sterilization monitoring page collects the consumables that sit around either cycle type.
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers case pricing and account setup, and the B2B wholesale collection lists the lines stocked for institutional buyers. Reselling? become a distributor.
References
- ISO 11138-5:2017 — Biological indicators for LTSF processes (checked 24 October 2026)
- ISO 25424:2018 — Low temperature steam and formaldehyde sterilization (checked 24 October 2026)
- ISO 11138-3:2017 — Biological indicators for moist heat (checked 24 October 2026)
Not sure how this applies to your own setup? Ask a sterilization compliance specialist — you’ll get a written answer specific to your equipment and province, with the regulation or standard cited.
Related Reading
- ISO 25424: low temperature steam and formaldehyde sterilization
- ISO 11138 series explained: what parts 1, 2, 3 and 4 actually require
Frequently Asked Questions
Can a steam biological indicator be used in an LTSF cycle?
No. A spore test labelled to ISO 11138-3 is qualified against moist heat at steam temperatures, while an LTSF cycle uses a formaldehyde and steam mixture below ambient pressure and needs an indicator qualified to ISO 11138-5.
What has to appear on an ISO 11138-5 certificate?
The test organism, the spore population per carrier, the D-value at the labelled conditions, the lot number and the expiry date. If the certificate does not name the LTSF process, treat the indicator as unqualified for that cycle.
Is ISO 11138-5 the same as ISO 25424?
No. ISO 11138-5 covers the biological indicators; ISO 25424 covers development, validation and routine control of the LTSF process. The 2017 edition of 11138-5 still points readers to ISO 14937 for validation, so cite ISO 25424 when describing the process.
How often does an LTSF unit need a spore test?
There is no single national answer in Canada. Frequency comes from the sterilizer instructions, provincial infection-control guidance and the procedure you write against CSA Z314:23. Do not copy a steam-cycle daily rule onto an LTSF unit without checking what it covers.
Last updated: October 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334).
0 comments