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ISO 11737-3

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ISO 11737-3

ISO 11737-3 is the standard published by the International Organisation for Standardisation (ISO) entitled ‘Sterilisation of healthcare products – Microbiological methods – Part 3: Testing for bacterial endotoxins”, i.e. “Sterilisation of healthcare products – Microbiological methods – Part 3: Bacterial endotoxin test”. The current edition is ISO 11737-3:2023 (first edition).

Note on regulatory status: This standard defines the requirements for method suitability, routine use and validation of bacterial endotoxin tests in the assessment of the biological safety of medical devices and in sterilisation processes. It provides a framework that is compatible with the pharmacopoeia methods (USP <85>, EP 2.6.14, JP 4.01); however, its focus is specifically on medical devices (for pharmaceutical products, the pharmacopoeia texts apply). It is applied in conjunction with the EU Medical Devices Regulation (MDR 2017/745) and the standard ISO 10993-11. This standard replaces the version ISO 11737-3:2004 published in previous years; the current version and the status of national implementation should be checked before submitting an application to the competent authorities.

Classification within the ISO 11737 series

The ISO 11737 series, comprising three parts, covers methods for the microbiological evaluation of medical devices:

  • ISO 11737-1: Determination of microbial load (bioburden)
  • ISO 11737-2: Sterility testing
  • ISO 11737-3: Testing for bacterial endotoxins

Together with sterilisation validation (ISO 11135, ISO 11137, ISO 17665, ISO 14937) and biological evaluation (ISO 10993 series), form a comprehensive system for ensuring sterility and safety.

Basic principles and methods

ISO 11737-3 is based on the Limulus amebocyte lysate (LAL) methods for the determination of lipopolysaccharides (endotoxins) derived from the cell walls of Gram-negative bacteria. In accordance with the pharmacopoeia methods, three basic groups of methods are defined:

  • Gel-Clot method: threshold test and semi-quantitative method; visual assessment of gel formation in a lysate-endotoxin mixture
  • Turbidimetric method: Photometric measurement of the change in turbidity resulting from coagulation (kinetic or end-point)
  • Chromogenic method: Photometric measurement of the coloured product formed by the degradation of a synthetic substrate via the coagulation cascade (kinetic or end-point)
  • Alternative methods: Methods based on recombinant factor C (rFC) and other validated alternatives; where permitted by the standard, these may be used subject to appropriate validation

Device-specific requirements and critical concepts

  • Sample preparation: Proper extraction of the device or its components, taking into account surface area, mass and contact conditions
  • Endotoxin limit (EL): A limit value determined according to the nature and duration of contact with the product (in accordance with ISO 10993-11 and the relevant regulatory guidelines)
  • Maximum valid dilution (MVD): MVD = (EL × sample concentration) / λ
  • λ (Lambda): Labelled sensitivity of the lysate (EU/ml)
  • CSE (Control Standard Endotoxin): A control standard calibrated against the reference standard (RSE)
  • Method suitability: evaluation of the interference test (inhibition/potentiation) and PPC recovery; instrument-specific validation
  • PPC (Positive Product Control): Confirmation of recovery based on a known quantity of endotoxin in the sample
  • Routine testing and monitoring: Routine assessment of production batches following validation
  • Revalidation: Re-evaluation following changes to the device design, materials, manufacturing process or sterilisation

The key parameters reported in the study are as follows:

  • Description of the device, type and duration of contact, and endotoxin limit (EL)
  • LAL method and mode used (gel cluster, turbidimetric, chromogenic; if an alternative method is used: validation summary)
  • Lysate batch, λ value and manufacturer’s specifications
  • CSE/RSE calibration and validation data
  • MVD and applied dilutions
  • Results of the method suitability/interference tests (PPC recovery, acceptance range)
  • Results of the negative and positive controls
  • Results of routine tests and comparison with EL
  • Version of ISO 11737-3 used and corresponding pharmacopoeia references
  • Data on measurement uncertainty and repeatability

Why is this being done?

ISO 11737-3 is used for the following scientific and regulatory purposes:

  • Assessment of the safety of medical devices: Demonstration that endotoxin contamination in products that come into contact with blood, solutions or tissue (e.g. infusion sets, catheters, implants, wound care products) is within the limit values
  • MDR compliance: Provision of the necessary data to ensure biological safety and sterility in accordance with the EU Medical Devices Regulation (2017/745)
  • Integration with ISO 10993-11: Conducting endotoxin tests as part of the assessment of material-related pyrogenicity
  • Integration into sterilisation validation: verification of the efficacy of depyrogenation processes; monitoring of the endotoxin load following sterilisation
  • Control of the production process: monitoring the endotoxin load of raw materials, intermediate products and finished products; assessment of the impact of process changes
  • Routine quality control: Assessment of production batches prior to market launch
  • Pharmacopoeia compliance: Where applicable, use of methods in accordance with USP <85>, EP 2.6.14 and JP 4.01 in the context of medical devices
  • Use of alternative methods: introduction of rFC-based and other validated alternatives following appropriate validation; reduction in the use of animal-derived LAL sources
  • Animal welfare (3Rs): Use of LAL and rFC methods as alternatives to the pyrogen test on rabbits
  • Approach to assessing the strength of evidence: Contribution to the holistic assessment of the product based on data relating to sterility (ISO 11737-2), microbial contamination (ISO 11737-1), biocompatibility (ISO 10993 series) and pyrogenicity

ISO 11737-3 detects bacterial endotoxins exclusively; material-related pyrogenicity (non-endotoxic pyrogens) and microbial contamination fall outside the scope of this standard and must be assessed using appropriate methods (rabbit pyrogen test, monocyte activation test, sterility test).

At NanoTest, we carry out bacterial endotoxin tests in accordance with ISO 11737-3 with scientific rigour, within the framework of our accredited laboratory infrastructure and our quality management system.

For information on method selection, method suitability and preliminary testing, MVD calculation, sample preparation, as well as routine monitoringand reporting processes in connection with your bacterial endotoxin tests in accordance with ISO 11737-3, please feel free to contact NanoTest.

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