Endotoxin testing for critical water in compliance with ANSI/AAMI ST108:2023
Reprocessing of medical devices aims to restore them to a quality appropriate for their normal use in patient care. Recently, ANSI/AAMI ST108:2023 – Water for the processing of medical devices has replaced AAMI TIR34:2014 – Water for reprocessing of medical devices. But do not let the minor title change lull you into a false sense of security. Whilst AAMI TIR34:2014 was an advisory document offering guidance for the quality of water used for medical device reprocessing, ANSI/AAMI ST108 contains binding regulatory requirements for water used in sterile processing, including those for endotoxin monitoring and limits.
This article highlights key elements of the ANSI/AAMI ST108:2023 standard and describes how the αBET™ system can support reliable endotoxin testing and robust quality assurance for critical water.
What changed?
ANSI/AAMI ST108:2023 mandates a shift from ‘Utility’ (tap) water to ‘Critical water’ as rinse water when processing high-risk medical devices, e.g., when medical devices come into contact with blood or cerebrospinal fluid. This is accompanied by a mandated endotoxin testing frequency and limits for critical water, impacting critical water production and in-use locations.
What is critical water?
Critical water is a highly purified form used for final rinses of medical devices or steam generation. To achieve the required level of purity, it typically undergoes multiple treatment steps such as reverse osmosis, deionisation, and ultrafiltration. These processes remove microorganisms, endotoxins, and other contaminants that could compromise device processing and downstream sterilisation efficiency.
What regulatory endotoxin limits apply?
ANSI/AAMI ST108:2023 specifies that critical water should not exceed 10 EU/mL. This limit provides a benchmark to verify system performance, guide routine testing and ensure consistent regulatory compliance.
Recommended endotoxin testing practices
The ST108 standard requires a documented water quality monitoring programme to verify that it meets defined specifications. The frequency of testing should be based on risk assessment, system design, and historical performance data.
Typical monitoring activities include:
Testing during installation and qualification
Routine checks of water distribution loops
Additional monitoring following maintenance or system modifications
Increased testing after microbial excursions or adverse trends
Validated detection methods should be used with appropriate controls and sampling locations throughout the water distribution network. Trending results over time help identify early signs of deterioration and inform corrective action [2,3].
Achieving accurate endotoxin testing with the αBET™ system
The αBET™ system provides a regulatory-aligned platform for reliable endotoxin testing in critical water. Using proprietary near-infrared optical detection, the platform delivers reproducible results whilst minimising analytical variability and supporting comprehensive, audit-ready documentation.
Key benefits include:
Quantitative testing suitable for routine water monitoring
Simplified workflows that improve efficiency
It can run fully Pharmacopoeia-compliant assays
It is fast. At 10 EU/mL, testing time is ~4 minutes
Reduced reagent consumption and operational costs
FDA Part 11-ready software for secure data integrity
Maintaining compliance with ANSI/AAMI ST108:2023
Control of endotoxins in critical water is essential for reliable medical device processing. ANSI/AAMI ST108:2023 establishes clear guidance on acceptable endotoxin limits and monitoring practices. A robust water quality management programme, supported by accurate endotoxin detection technology such as the αBET™ system, enables organisations to achieve regulatory compliance and maintain operational confidence across all water-dependent processes.
Contact us today to schedule a discovery call and learn how the αBET™ system can optimise endotoxin control and ensure compliant water quality.