ISO 11138 Series Explained: What Parts 1, 2, 3 and 4 Actually Require

Quick facts: ISO 11138 is a multi-part international standard for biological indicators, organised by sterilant rather than by product. Part 1 holds the general requirements that every indicator inherits; Part 2 covers ethylene oxide, Part 3 covers moist heat, Part 4 covers dry heat and Part 5 covers low-temperature steam and formaldehyde. Part 7 is guidance for selection, use and interpretation, and Part 8 defines how a reduced incubation time is validated. The series sets indicator performance, not monitoring frequency — frequency comes from your regulator.

If you have ever tried to compare two spore test quotes and found that neither supplier cites the same part number, the ISO 11138 series is why. It is a standards family, not a single document, and each part carries a different obligation for a different sterilant. The practical consequence is that the phrase "ISO 11138 compliant" on a product page tells you almost nothing until you know which part is being claimed, who that part binds, and whether the claim covers manufacture or just intended use. This guide walks Parts 1, 2, 3 and 4 clause group by clause group, and then resolves the one question Canadian buyers ask most often: whether a biological indicator has to be incubated in its own brand of incubator.

What the ISO 11138 series actually is

The series sits under ISO Technical Committee 198, Sterilization of health care products. Its structure is deliberate: one general part, one part per sterilant, and supporting parts for guidance and for validation of shorter incubation times.

One structural point matters more than the others. Parts 2 through 5 do not replace Part 1 — they extend it. A steam indicator is therefore governed by Part 1 plus Part 3, and an EO indicator by Part 1 plus Part 2. When a supplier says a product is compliant, the useful follow-up question is which parts, and whether the claim is about the indicator as manufactured or about the sterilant it is intended to monitor. If no later part exists for a given process, the scope of Part 1 states that the general document applies on its own.

Part 1: the general requirements every indicator inherits

The scope of ISO 11138-1:2017 covers general requirements for the production, labelling, test methods and performance characteristics of biological indicators, including inoculated carriers and suspensions and their components, for use in validation and routine monitoring of sterilization processes. That sentence is worth reading twice, because it places the bulk of the obligation on the producer rather than on the clinic.

The document is organised into seven numbered clauses and six annexes, four of them normative. That internal structure is the most useful thing a buyer can know, because each clause group answers a different question.

Two of those entries are routinely misread. Annex B is the one that explains why a carrier or a packaging material can suppress spore recovery even when the cycle was adequate — growth inhibition is a property of the indicator, not of the sterilizer. Annex E is the one to cite when a supplier is asked to justify a survival time and a kill time; those figures come from a defined calculation, not from a marketing estimate.

The practical output of all this is a certificate of analysis. A meaningful BI certificate declares the test organism, the nominal population per unit, the D-value at a stated temperature, the z-value, and a lot number that ties back to the production record. If a quote arrives without those fields, the standard number attached to it is decorative.

Parts 2, 3 and 4: what changes by sterilant

The process-specific parts all follow the same pattern — test organisms, suspensions, inoculated carriers, indicators, test methods — but the numbers and the organisms differ, and those differences are what make an indicator suitable for one sterilizer and unsuitable for another.

Part 4 is the one most often skipped in Canadian dental content, and it is instructive. Commercial dry heat indicators compliant with ISO 11138-4 are supplied as a filter paper strip inoculated with Bacillus atrophaeus spores and packaged in a glassine pouch, with a declared population of 10⁶ colony-forming units per unit and a stated D-value at 160 °C. That is a very different set of numbers from a steam indicator, and it demonstrates the central point of the series: an indicator is only meaningful against the process it was built for. A steam indicator validates nothing about a dry heat oven.

Manufacturer duties versus user duties

This is the distinction that resolves most procurement arguments. The ISO 11138 series is often described as a clinic standard. It is mostly not one.

ISO 11138-7:2019 carries the user-side expectations. Its own text is blunt about why the details matter: "the incubation procedure used after exposure to the process, including incubation temperature and culture medium type, supplier and specific batch, can affect measured resistance as a function of recovery and growth." The same clause set states that "the recommendations of the biological indicator manufacturer for transportation, storage and use should be followed," and that after exposure, "the aseptic transfer (if applicable) and incubation of biological indicators as specified by the biological indicator manufacturer is critical for obtaining correct results." The document also confirms that self-contained indicators are designed to remove the need for aseptic handling, because the recovery medium sits inside the primary package and the package need not be opened. Part 7 reserves dedicated sections for incubation temperature, incubation period and choice of growth medium, and separately for placement, process challenge devices, and interpretation and acceptance criteria.

The incubation question: what the standard does and does not require

Across the series, the variable that governs incubation is temperature — not brand. The indicator's instructions state a temperature band, and Part 7 directs the user back to those instructions. Nowhere does the series require the incubator and the indicator to share a manufacturer.

Manufacturer documentation makes this concrete. In the Mesa Labs EZTest instructions for use, the incubation section states plainly that "any microbiological incubator that is adjusted for 55 - 60 °C will satisfy the incubation conditions for the EZTest," with the same document requiring incubation of the indicators for 24 hours at 55 °C to 60 °C for final verification, and noting that the indicators in the test packs are manufactured under quality systems in compliance with ANSI/AAMI/ISO 11138. SteriTec's EZTest instructions, distributed by Getinge, list the same conditions — an incubation temperature and time of 24 hours at 55 °C to 60 °C, with a standards classification of ANSI/AAMI/ISO 11138.

That is the honest reading of the temperature rule, and it comes with a boundary that is frequently left out of the discussion. The temperature rule applies to indicators whose result is read as a colour change against a stated incubation period. It does not apply to rapid, instrument-read systems. Rapid readout is a reduced incubation time, and a reduced incubation time is itself a validated claim: ISO 11138-8:2021 specifies the standardised test method used to establish or confirm a reduced incubation time for indicators monitoring moist heat and EO processes. In practice that validation binds one indicator to one reader, because the instrument is calibrated to the fluorescence kinetics of that specific indicator and the shorter period has been demonstrated only for that pairing. So the accurate statement is narrower than "brands are interchangeable" and broader than "you must stay in one ecosystem": for conventional colour-change spores, temperature is what matters; for instrument-read rapid systems, the validated pairing is what matters.

Why this matters in Ontario and across Canada

None of the ISO 11138 parts set a monitoring frequency, and clinics sometimes assume a standard number implies a schedule. In Ontario, the RCDSO requires a biological indicator placed in a process challenge device for each sterilizer on every day that it is used, and for each type of cycle used. Weekly monitoring is the CDC and AAMI ST79 baseline applied in most US states — useful as a comparison point, and only as a comparison point, when describing Canadian obligations.

Canada's national sterilization standards are a separate layer again. The CSA Z314 series requires a sterilisation assurance system and biological monitoring, but it does not dictate how often a clinic must test; frequency is set by provincial regulators and by institutional policy. That is why two clinics in different provinces can both be compliant with the same indicator standard and still run different monitoring schedules. The indicator standard answers "is this spore test built to a defined performance specification?" The regulator answers "how often, on which sterilizer, and with what documentation?"

How to verify a compliance claim before you buy

• Ask which parts of ISO 11138 the product is declared against — for a steam indicator, expect Part 1 and Part 3 to be named.
• Ask for the certificate of analysis and confirm it carries the organism, nominal population, D-value, z-value and lot number.
• Confirm the declared incubation temperature and period match the equipment you intend to use, whether that is a dry-block incubator such as the 24-hour dry-block incubator or a rapid reader.
• If the indicator is a rapid, instrument-read product, confirm that the reduced incubation time is validated for that indicator and that reader as a system.
• Confirm the certificate covers the sterilant you actually run. An EO certificate means nothing for a steam cycle.
• Check that your monitoring log records what the regulator expects, including the cycle type, the sterilizer and the result.

For clinics that want a single reorder point across monitoring consumables, the sterilization monitoring range groups indicators, incubators, readers and daily vacuum test packs together. A 25-pack of 24-hour self-contained indicators covers a single sterilizer running daily monitoring for roughly a month of clinic days, which is the volume question worth solving before the standard-number question. CliniEco Medical supplies these lines under MDEL #35334.

If your sterilizer runs daily, the fastest way to verify that your monitoring routine produces readable results is a 5-pack biological indicator trial rather than a full case order.

Related reading

• ISO 11138 series: BI standards for steam, EO and vapour processes explained — the short orientation to the series.
• Locked into one BI brand? Why your spore tests do not have to be — the switching decision in full.
• D-value, z-value and SAL: the numbers behind sterilization validation — how the certificate figures are calculated.
• Self-contained BIs versus spore strips and ampoules — format differences and aseptic handling.
• Industrial sterilization verification in Canada — the same series applied outside healthcare.
• Sterilization compliance hub — the full set of monitoring and record-keeping guides.
• sterilization record-keeping tool

Frequently Asked Questions

Does ISO 11138-1 apply if a later part covers my sterilizer?
Yes — read both. Part 1 sets the general requirements and the normative annexes for population, D-value and survival-kill determination; the process-specific part adapts those requirements to your sterilant and supplies the process-specific numbers.

Can a biological indicator from one brand be incubated in another brand's incubator?
For conventional colour-change indicators, the governing condition is the temperature band stated on the indicator label. Mesa Labs states in its EZTest instructions for use that any microbiological incubator adjusted for 55-60 °C will satisfy the incubation conditions. Rapid fluorescent systems are the exception: indicator and reader are validated together under a reduced incubation time.

What does reduced incubation time mean, and which part covers it?
It is a shorter post-exposure incubation validated to give the same result as the full period. ISO 11138-8:2021 specifies the test method for establishing or confirming a reduced incubation time for indicators monitoring moist heat and EO processes.

Does ISO 11138 set how often a clinic must run a spore test?
No. The series defines the indicator, not the schedule. In Ontario the RCDSO requires a biological indicator in a process challenge device for each sterilizer on every day it is used and for each cycle type used. Weekly monitoring is the CDC and AAMI ST79 baseline seen in most US states.

What is the difference between a D-value and a z-value?
The D-value is the exposure time at a stated temperature that reduces the population by one log. The z-value is the temperature change that alters the D-value tenfold. ISO 11138-1:2017 provides normative methods in Annex C (survivor curve), Annex D (fraction-negative) and Annex E (survival-kill response).

Are the requirements aimed at the clinic or the manufacturer?
Mostly the manufacturer. Manufacturing requirements, population and resistance determination, culture conditions and the normative annexes describe what the producer must do and declare. The user-side obligations — storage, handling, incubation as instructed, placement and interpretation — sit in ISO 11138-7:2019.

Sources

• ISO 11138-1:2017, Sterilization of health care products — Biological indicators — Part 1: General requirements — iso.org/standard/66442.html
• ISO 11138-2:2017, Part 2: Biological indicators for ethylene oxide sterilization processes — iso.org/standard/66445.html
• ISO 11138-4:2017, Part 4: Biological indicators for dry heat sterilization processes — iso.org/standard/66447.html
• ISO 11138-5:2017, Part 5: Biological indicators for low-temperature steam and formaldehyde sterilization processes — iso.org/standard/66448.html
• ISO 11138-7:2019, Part 7: Guidance for the selection, use and interpretation of results — iso.org/standard/74113.html
• ISO 11138-8:2021, Part 8: Method for validation of a reduced incubation time for a biological indicator — iso.org/standard/62337.html
• ANSI/AAMI/ISO 11138-1:2017 preview copy, including the contents and annex list — my.aami.org
• Mesa Labs, EZTest biological test pack instructions for use (incubation at 55-60 °C; manufacture in compliance with ANSI/AAMI/ISO 11138) — mesalabs.com
• SteriTec EZTest steam biological indicator instructions (24 hours at 55-60 °C; ANSI/AAMI/ISO 11138 classification), distributed by Getinge — getinge.com
• Crosstex, biological indicators compliant with ISO 11138-4 for dry heat — crosstex.com
• SSI Diagnostica, dry heat biological indicator specifications (10⁶ per unit; D-value at 160 °C) — ssidiagnostica.com
• Royal College of Dental Surgeons of Ontario, Infection Prevention and Control standard, guidelines and resources — rcdso.org

Related Reading

Explore more guides in this category:

• Biological Indicator Kill Time Explained: What the Incubation Window Means
• Diapers for Seniors in Edmonton: Supply Planning for Caregivers and Facilities
• Opening a Dental Clinic in Ontario: The Complete 90-Day Compliance and Supply Plan