A chemical indicator strip is a carrier - usually paper or coated card - printed or impregnated with an indicator ink. The ink is the active part: it changes irreversibly when the strip is held at the conditions the cycle is designed to deliver. What it reports is what happened where it was placed, not what happened to the instrument inside the wrap.
What is actually on a chemical indicator strip?
Two things sit on the strip: the substrate that holds the chemistry, and the indicator ink itself, chosen so that it changes appearance once the strip has seen the variables it was built to detect. The change is irreversible, so an indicator cannot be reset by cooling a pack back down.
The classes differ mainly in what the ink responds to. ISO 11140-1:2014 defines them, and Public Health Ontario reproduces the same international table in its provincial PIDAC guidance for cleaning, disinfection and sterilization in health care settings (Table 2, printed page 39).
| Class | What the indicator chemistry responds to | What a change on the strip tells you |
|---|---|---|
| Class 1 | A single process variable, to mark items as processed | The item went through a cycle - tape, label or load card on the outside of a pack. |
| Class 4 | Two or more critical variables inside a stated range | The strip saw a combination of conditions, so it is a multi-variable read. |
| Class 5 | All critical variables - time, temperature and the presence of steam | An integrating indicator, with stated values correlated to a biological indicator at three time and temperature relationships. |
| Class 6 | All critical variables for one specified cycle | An emulating indicator matched to a particular cycle time and temperature, such as 121 °C for 30 minutes. |
A strip is therefore not a generic sterilization test: Public Health Ontario notes that a different Class 6 indicator is required for each sterilization cycle time and temperature used, while a Class 4 strip covers a stated range.
How do you read the change, and when is a partial change a fail?
Read the strip against its endpoint, not against "some colour". The Ontario guidance requires an internal chemical indicator inside every package or bundle, in the area judged least accessible to the steam, plus an externally visible Class 1 indicator on each package.
| What you see | What it means | What to do |
|---|---|---|
| The ink reaches its endpoint at the monitored area | The conditions the indicator was designed to detect were reached where the strip sat | Record the result against the load |
| The change is partial, blotchy or short of the endpoint | The indicator did not reach its endpoint - it is not a pass | Treat the load as not released and investigate the cycle |
| No visible change at all | The strip never saw the cycle conditions | Do not release the load |
| Change after dry heat or an oven cycle | The chemistry was matched to steam, not dry heat | The reading is not usable as steam monitoring |
The same guidance adds that indicators must be used only for the sterilizer type and cycle for which they were designed and validated, must be interpreted by trained staff, and must not be used beyond their expiration date.
Do indicator strips expire, and how should they be stored?
Yes. The indicator chemistry reacts to heat, humidity and light, so storage matters as much as the printed expiry date. Indicators are stored in accordance with the manufacturer's instructions, and those instructions are the authority on the temperature and humidity window for a particular product. A strip left open on a bench, or stored next to a sterilizer, can change early or unevenly - and either behaviour destroys the value of the read.
Do you still need tape and a spore test as well?
Yes - three types of monitoring answer three different questions. The external Class 1 indicator shows an item was processed. The internal chemical indicator shows the conditions were reached at the least accessible point in the pack. The biological indicator shows whether the cycle actually killed a resistant organism. Public Health Ontario states that chemical indicators do not replace the need to use a biological indicator, and adds that a Class 5 or Class 6 indicator with the cycle's physical parameters may be used to justify releasing routine loads when a load cannot be quarantined until the spore result is available. That release route is a documented exception, not the default.
A clinic that wants the strip result, the load, the cycle and the spore test in one record can build it from the printable sterilization log sheet, which follows the load, service, malfunction and package-label fields. The same page carries a log and package-label generator for teams that would rather type the fields than fill them by hand.
Have a question about your own facility? Send it in and you will get a written answer specific to your setup, with the regulation or standard it is based on cited. Ask your compliance question.
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.
Chemical indicator strip content decides what a strip can and cannot show, and no strip chemistry proves sterilizing conditions on its own. Clinics, long-term care homes and labs in Canada can apply for a free 5-pack of 24-hour biological indicators, with shipping covered: free 5-pack of biological indicators.
Where to Buy Biological Indicators in Canada
CliniEco Medical supplies these from Ontario with published CAD pricing (MDEL #35334) — no quote required, and each pack ships with the lot number printed on it so your monitoring record stays traceable.
| Format | Pack size | Price (CAD) | |
|---|---|---|---|
| 24-hour self-contained | 25-pack | $84.99 | Order |
| 24-hour self-contained | 100-pack | $299.00 | Order |
| 3-hour rapid fluorescence | 50-pack | $274.99 | Order |
Round Out Your Sterilization Setup
A biological indicator is one link in the chain — these are the pieces it works with:
- Sterilization pouches — Class 4 dual-indicator, 200-pack — the packaging the indicator rides inside
- Autoclave indicator tape — 3-roll set — the external chemical indicator on every pack
- Sterilization roll — 50 m pre-cut sheets for larger instruments
- Constant-heat pouch sealer — 200 °C, 12 mm seal — for consistent pouch closures
Which format does your sterilizer actually need?
Match the readout time to how fast you need the result: a 24-hour self-contained indicator works in any gravity or pre-vacuum cycle with a standard incubator, while a 3-hour fluorescence tube needs the matching reader. Running one cycle type per day, the 25-pack covers a month; busier clinics move to the 100-pack and cut the per-test cost.
How much do spore tests cost in Canada?
Published pricing runs $3.40 per test on the 25-pack down to $2.99 on the 100-pack — no distributor quote, no account needed.
Not sure which format your sterilizer needs? Generate a free sterilization log sheet first — it maps your cycles and tells you the pack size that fits. Questions about your setup? Ask a Compliance Specialist.
Related reading
- Chemical indicator strips vs integrators: what each one proves
- How autoclave tape chemistry works: what the colour change actually measures
- Chemical indicator strips vs autoclave tape: which belongs in the sterilization log?
Frequently Asked Questions
Is the ink the same on every type of indicator strip?
No. The class describes what the chemistry responds to, so a Class 1 process indicator and a Class 6 emulating indicator are built differently and are not interchangeable.
Can a strip change colour and still be a fail?
Yes. A change that falls short of the indicator's stated endpoint is not a pass, even though the strip looks different from a new one. Read the endpoint, not the presence of colour.
Do strips need to be kept in their original packaging?
They should be stored as the manufacturer instructs and used within the printed expiry date, because the chemistry reacts to heat, moisture and light.
Does a passing strip mean the instruments are sterile?
No. A chemical indicator shows the conditions it detects were reached where it was placed. Sterility assurance comes from the biological indicator.
Can one type of strip cover every cycle?
Not a Class 6 emulating indicator, which is matched to one cycle time and temperature, so a clinic running more than one steam cycle needs a matching indicator for each.
CliniEco Medical holds Medical Device Establishment Licence MDEL #35334. This article summarises published national and provincial guidance for information only; it does not replace the sterilizer or indicator manufacturer's instructions, or the requirements of the regulator that applies to a practice setting.
Sources
- ISO 11140-1:2014, Sterilization of health care products - Chemical indicators - Part 1: General requirements (preview)
- Public Health Ontario, PIDAC guidance for cleaning, disinfection and sterilization (PDF, Table 2, p.39)
- Centers for Disease Control and Prevention, Guideline for Disinfection and Sterilization in Healthcare Facilities
- Solventum (3M), Comply steam chemical indicator strips 1250
- Terragene, Integron IT26-1YS chemical integrator for steam
- CliniEco Medical, Steam Chemical Integrator - Class 5, ISO 11140-1 Type 5
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