ISO 11138-5:2017

Overview

ISO 11138-5:2017 - "Sterilization of health care products - Biological indicators - Part 5" - specifies requirements for biological indicators, inoculated carriers, suspensions, test organisms and test methods used to assess low‑temperature steam and formaldehyde sterilization processes. The standard defines how biological indicators are produced, characterized and tested so users can reliably evaluate sterilizer performance where steam plus formaldehyde is the sterilizing agent.

Key topics and technical requirements

• Test organism: Specifies spores of Geobacillus stearothermophilus (or other strains of demonstrated equivalent performance) as the primary test organism for these processes.
• Resistance characterization: Resistance is expressed as a D value (minutes) at 60 °C, reported to one decimal place. Each batch/lot must state the D value and viable-count characteristics according to ISO 11138‑1 requirements.
• Population and reporting: The standard requires defined procedures for reporting viable counts and survival/kill response windows to allow batch comparison and meaningful interpretation.
• Carrier and packaging suitability: Materials used for carriers and primary packaging must be demonstrated suitable for low‑temperature steam/formaldehyde exposure; some materials (e.g., certain filter papers) may be unsuitable because of formaldehyde chemisorption.
• Annex A - Liquid‑phase resistance test (normative): Details a reproducible immersion test in an aqueous formaldehyde solution (defined molarity, maintained at 60 °C with strict timing and temperature control) using test tubes in a water bath. Test parameters, neutralization, recovery media and validation of the method are specified to ensure repeatability.
• Annex B - Rationale: Explains why a liquid‑phase method is preferred (gas‑phase formaldehyde concentrations are unstable and condensate concentrates formaldehyde), supporting reproducible determination of indicator resistance.

Practical applications and users

ISO 11138-5:2017 is used by:

• Manufacturers of biological indicators and inoculated carriers to design, validate and label products for low‑temperature steam/formaldehyde processes.
• Sterilization validation engineers and test laboratories performing resistance testing and routine control of sterilization cycles.
• Medical device manufacturers and sterile processing departments that need validated biological indicators for process monitoring and routine assurance.
• Regulators and quality auditors referencing standardized requirements for sterility assurance and indicator performance.

Practical value: the standard enables consistent, reproducible assessment of low‑temperature steam/formaldehyde sterilization efficacy and supports reliable selection and interpretation of biological indicator results.

Related standards

• ISO 11138‑1 (general requirements for biological indicators)
• ISO 14937 and ISO 25424 (requirements for validation and control of sterilization processes)
• ISO 14161 (guidance on selection, use and interpretation of biological indicators)
• EN 14180 (requirements for low‑temperature steam/formaldehyde sterilizers)