ISO 11138-8:2021

Overview

ISO 11138-8:2021 specifies a standardized test method to establish or confirm a Reduced Incubation Time (RIT) for biological indicators (BIs) used to monitor moist heat and ethylene oxide (EO) sterilization processes. The standard provides requirements to validate an incubation period shorter than the 7-day reference incubation time in ISO 11138-1:2017. It is intended for BI manufacturers and end users who need to establish, validate, or confirm an RIT as part of their quality system.

Key topics and technical requirements

• Scope and exclusions
  • Applies only to BIs for moist heat and EO sterilization (EO RIT applies to 100% EO or EO blends regardless of load).
  • Does not cover dry heat, low temperature steam formaldehyde (LTSF), or vaporized hydrogen peroxide (VH2O2).
• Test equipment and exposure
  • Exposures must be performed in a resistometer meeting ISO 18472 or a sterilizer with fully specified, controlled, repeatable parameters.
• Sample size and selection
  • Minimum of 100 BIs from each of 3 different lots (min. total 300 BIs).
  • Samples should be prepared and positioned to avoid shielding and ensure uniform exposure.
• Fractional cycle selection
  • Choose fractional cycle conditions that produce 30%–95% positive BIs after the 7-day incubation; repeat if outside this window.
• Incubation and monitoring
  • Incubate per BI instructions for 7 days and record positive/negative results at predetermined intervals (days, hours, etc.).
  • Maintain consistent timing between exposure end and initiation of recovery.
• RIT determination
  • For each lot and fractional cycle, identify the shortest time where positives at that interval correlate ≥97% with 7-day positives.
  • The most conservative (longest) time across all tested lots and cycles is assigned as the RIT.
• Design and end-user guidance
  • Method applies to BIs where primary components include a spore carrier and a specified recovery medium (kit or self-contained BI).
  • End users may rely on manufacturer-validated RIT if they use the same sterilant and incubation temperature; otherwise, they must validate RIT per this method.

Applications and who uses this standard

• BI manufacturers validating reduced incubation claim for commercial products.
• Sterilization QA teams in hospitals, dental clinics, and outpatient facilities needing faster BI results for product release.
• Clinical engineering and sterilization validation teams implementing quality systems and routine lot-to-lot verification.
• Useful for regulatory documentation, product labeling, and establishing faster turnaround for sterilization monitoring while maintaining reliability.

Related standards

• ISO 11138-1:2017 (reference incubation time and BI general requirements)
• ISO 11138 series (biological indicators)
• ISO 11138-7:2019 (use of self-contained BIs)
• ISO 18472 (resistometer requirements)

Keywords: ISO 11138-8:2021, reduced incubation time, RIT validation, biological indicators, moist heat sterilization, ethylene oxide sterilization, BI manufacturer, sterilization quality assurance.