Overview
EN ISO 11138-4:2017 - "Sterilization of health care products - Biological indicators - Part 4: Biological indicators for dry heat sterilization processes" - specifies production, test methods and performance requirements for biological indicators (BIs) used to validate and monitor dry heat sterilization (120 °C to 180 °C). Adopted by CEN as EN ISO 11138-4:2017, this edition supersedes the 2006 version and provides updated criteria for BI manufacture, resistance characterization and packaging suitability.
Key topics and technical requirements
- Test organisms: Spores of Bacillus atrophaeus (or equivalent strains with demonstrated performance).
- Population: Inoculated carriers and BIs must contain ≥ 1.0 × 10^6 viable spores per unit.
- Resistance metrics:
- D value (decimal reduction time) is reported at 160 °C, to one decimal place; minimum D ≥ 2.0 min for B. atrophaeus when tested per Annex A.
- z value (temperature change for tenfold change in D) must be determined from at least three temperatures in the 150–180 °C range and z ≥ 20 °C (see Annex B for calculation).
- Test methods and equipment: Determination of D and survival–kill characteristics requires a resistometer using the reference resistometer process parameters (Annex A). D values are determined per ISO 11138-1 annexes.
- Carrier and primary packaging suitability: Manufacturers must demonstrate carrier/packaging stability under specified exposure conditions (dry heat in ambient air), including a challenge at ≥ 5 °C above stated maximum and a minimum exposure time of 30 minutes; if no maximum temp is stated, assume ≥ 180 °C.
- Documentation: Resistance characteristics, viable counts (increments ≤ 0.1 × 10^n), and batch/lot D values must be declared with the BI.
Practical applications
- Validation and routine monitoring of dry heat sterilizers used for medical devices and healthcare products (e.g., glassware, metal instruments).
- Manufacture and quality control of biological indicators and inoculated carriers.
- Laboratory testing to determine BI D and z values for product specification and comparison.
- Supporting sterilization process qualification, performance qualification and ongoing process control.
Who should use this standard
- BI manufacturers and suppliers
- Medical device manufacturers performing sterilization validation
- Sterilizer and equipment manufacturers
- QA/Validation engineers and microbiology labs
- Hospital central sterile services and regulatory bodies
Related standards
- ISO 11138-1:2017 - General requirements for biological indicators (referenced for production and labelling)
- ISO 20857 - Validation and control of dry heat sterilization processes
- ISO 18472 - Test equipment for biological and chemical indicators
- ISO 14161 - Guidance on selection, use and interpretation of BI results
Keywords: EN ISO 11138-4:2017, biological indicators, dry heat sterilization, Bacillus atrophaeus, D value, z value, sterilization validation, medical device sterilization.
