ISO 25424:2018

Overview - ISO 25424:2018 (LTSF sterilization for medical devices)

ISO 25424:2018 specifies requirements for the development, validation and routine control of low temperature steam and formaldehyde (LTSF) sterilization processes for medical devices. It covers sterilization processes that use a mixture of low temperature steam and formaldehyde as the sterilizing agent and that operate below ambient pressure. The standard is intended to ensure reproducible, reliable sterilization with documented sterility assurance through validated process design, monitoring and control.

Key technical topics and requirements

• Scope & exclusions: Applies to medical devices; excludes prion inactivation, designation of “STERILE” (see EN 556‑1), full QMS prescription, occupational safety, analytical residue methods and preparatory cleaning steps (see ISO 17664).
• Quality management elements: Documentation, management responsibility, product realization and control of non‑conforming product (linked to ISO 13485 and ISO 9001).
• Sterilizing agent characterization: Chemical and microbicidal behavior of the LTSF agent, material compatibility and environmental considerations.
• Process and equipment characterization: Definition of cycle parameters, equipment performance and installation requirements.
• Product and process definition: Determining product groups, load configurations and process limits based on bioburden and reference microorganisms.
• Validation framework: Installation Qualification (IQ), Operational Qualification (OQ) and Performance Qualification (PQ) - including physical, microbiological and desorption/drying aspects.
• Routine monitoring & control: Use of biological indicators, chemical indicators, records, product release criteria and ongoing maintenance/requalification.
• Change control and reassessment: Procedures for assessing changes to process, equipment or product that could affect sterility assurance.
• Informative annexes: Guidance on process definition, environmental aspects and normative annexes for microorganism inactivation approaches.

Practical applications and who uses ISO 25424

• Process developers designing LTSF sterilization cycles.
• Manufacturers of sterilization equipment specifying, qualifying and documenting equipment performance.
• Medical device manufacturers validating sterilization for new devices or revised packaging/configurations.
• Sterile services departments and contract sterilizers implementing routine control, biological/chemical indicator programs and product release.
• Regulatory and QA/validation teams preparing validation protocols, IQ/OQ/PQ documentation and change‑control evidence.

Practical use cases include validating new LTSF cycles, assessing material compatibility with formaldehyde, defining release criteria based on biological indicators, and establishing routine monitoring and requalification schedules.

Related standards (for reference)

• ISO 14937, EN 14180, ISO 11139, ISO 13485, ISO 17664, EN 556‑1, IEC 61010‑2‑040, ISO 22442.

Keywords: ISO 25424:2018, low temperature steam and formaldehyde, LTSF sterilization, medical device sterilization, validation, IQ/OQ/PQ, routine control, biological indicators, chemical indicators, sterility assurance.