What to Do When a Spore Test Result Is Inconclusive
What should you do when a spore test result is inconclusive?
An inconclusive spore test is not the same as a failed one, and treating it as a failure - or worse, as a pass - leads to the wrong response. An inconclusive result is a problem with the test itself, so nothing is proven either way. The load stays held, and the test is repeated properly.
What is the difference between an inconclusive, a failed and a passing result?
There are three outcomes, not two, and they call for different actions.
| Result | What it shows | What to do |
|---|---|---|
| Passing (negative) | No growth of the test organism; control grew as expected | Release on that basis, and record the result |
| Failing (positive) | Growth of the test organism; control grew as expected | Hold the load and investigate the cycle |
| Inconclusive (invalid) | No growth at all, or a control that behaved unexpectedly | Discard the result, hold the load, repeat the test |
The control is what separates the three. A biological indicator only means something when its built-in control behaves as the instructions say; if the control is wrong, the result is invalid whatever the test well shows.
What makes a result inconclusive?
Work through the usual causes. The control did not grow, which makes the whole test invalid. The indicator was incubated at the wrong temperature or time, or read in the wrong reader. It was past its expiry, or stored somewhere too hot or too cold. The vial was contaminated during handling. Each produces a reading that cannot be trusted, and the fix is the same: repeat with a fresh indicator, handled and incubated per its instructions.
What is the step-by-step response?
1. Hold the affected loads and mark them unreleased.
2. Read the control; if it did not behave as described, treat the whole test as invalid.
3. Check the incubation temperature and time against the indicator's instructions.
4. Check the expiry date and how the indicators have been stored.
5. Discard the invalid test and repeat with a fresh indicator.
6. If the repeat passes, release the load on that result and document both tests.
7. If the repeat gives a valid failed result, treat it as a genuine failure.
A one-hour rapid-readout biological indicator read in its matching fluorescence reader removes most of the handling steps that cause an invalid result. Where a facility uses a standard indicator, a dry-block incubator keeps the temperature steady, a common reason a control misbehaves.
Can loads be released while the test is repeated?
Not on an inconclusive result. The load is held until a valid test is read, or the facility follows its written policy for holding and recalling items. In Ontario, the RCDSO requires a biological indicator for each sterilizer on every day it is used.
When does an inconclusive result become a sterilizer problem?
The distinction matters for where time is spent. An inconclusive result is a testing error: fix the test and re-run it. A valid failed result is a sterilization problem: hold the load, review the cycle and the load, and watch the next cycles. Only the second points at the machine.
Working in a dental practice? See our dental practice sterilization monitoring supplies for the indicators, readers and incubators used for daily biological monitoring.
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 11138-1 - Biological indicators for sterilization (via Genorma) (checked 4 October 2026)
- RCDSO - Spore testing must be done each day the sterilizer is used (checked 4 October 2026)
Printable companion: the free sterilization log sheet lays out the fields an inspection asks for, so an invalid test is recorded as it is found.
The sterilization log generator then prints a record with the columns your reprocessing documentation needs.
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.
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
- Class 5 chemical integrators — 100-pack — the in-pack check that pairs with your biological indicator
- 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
- What to Do When a Spore Test Fails in Canada
- Autoclave Spore Test Log Fields: What to Record
- Autoclave Tape Inconclusive Result: What a Faded or Uneven Strip Tells You
Frequently Asked Questions
What does an inconclusive spore test result mean?
An inconclusive result cannot be read as pass or fail - usually because the control did not grow, the incubation was wrong, the indicator was expired or damaged, or the test was contaminated. It is a problem with the test, not proof that sterilization failed.
How do I tell an inconclusive result from a failed one?
A failed test shows growth of the test organism against a control that grew as expected. An inconclusive test usually shows no growth anywhere, or a control that did not behave as the instructions describe, so the result cannot be trusted.
When should the sterilizer itself be investigated?
When a repeat, correctly handled test gives a valid failed (positive) result. An inconclusive result points at the test first; a genuine failure points at the sterilizer, and that is when the cycle, the load and the machine are reviewed.
Last updated: October 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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