Endotoxin Testing: Methods, USP <85> Requirements, and Industry Implications

Endotoxin Testing performs a crucial role in the pharmaceutical and medical device industries for ensuring product safety and regulatory compliance.

by | May 6, 2024

Endotoxin testing is a critical quality control measure employed primarily in the pharmaceutical and medical device industries to ensure the safety and efficacy of products, especially those that come into direct contact with the human body. Endotoxins, primarily lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria, can cause severe immune responses even at low concentrations. This article explores the methods of endotoxin testing, the requirements set forth by the United States Pharmacopeia (USP) Chapter <85>, and the importance of these practices to industry.

Understanding Endotoxins

Endotoxins are part of the cell wall of Gram-negative bacteria that, when released during bacterial lysis or growth, can provoke pyrogenic responses in humans. Given their potential to cause fever, shock, and other severe health complications, the rigorous testing for these toxic substances in pharmaceutical products and medical devices is non-negotiable.

USP <85> Requirements

USP Chapter <85> “Bacterial Endotoxins Test,” provides standardized methods for the detection and quantification of endotoxins. The key requirements include:

  • Sensitivity and Validation: The test must be sensitive enough to detect endotoxins at a level that is considered safe for human exposure. The sensitivity, known as the Limulus Amebocyte Lysate (LAL) reactivity, must be validated against a standard endotoxin reference.
  • Method Suitability: Prior to routine testing, the chosen method must be validated for each product type to ensure no interference occurs from the product itself.
  • Sampling and Handling: Specific guidelines are provided for sample size, handling, and storage to prevent contamination or endotoxin loss.
  • Control Standard Endotoxin (CSE): Calibration of the assay is required using a Control Standard Endotoxin to ensure accuracy and precision.

Methods of Endotoxin Testing

There are primarily three methods endorsed by USP <85> for endotoxin testing, each based on the LAL test:

  1. Gel Clot Method:
    • Description: This method evaluates the formation of a gel clot in the LAL; a positive test indicates the presence of endotoxin.
    • Application: Used for products where interference is minimal and the simplicity of the assay is valued over high throughput or automation.
  2. Turbidimetric Method:
    • Description: This quantitative method measures changes in the turbidity (cloudiness) of the LAL mixture after endotoxin exposure.
    • Application: Suitable for bulk and final product testing where precise quantification is needed and can be automated for high-volume testing.
  3. Chromogenic Method:
    • Description: A quantitative test that involves the cleavage of a synthetic peptide-chromogen complex that changes color upon reaction with endotoxin.
    • Application: Highly sensitive and used for a wide range of products, including those that are prone to interference in the gel clot and turbidimetric tests.

Importance to Industry

The necessity of endotoxin testing in the pharmaceutical and medical device industries cannot be overstated:

  • Patient Safety: Ensures that injectable or implantable products are free from contamination that could lead to severe health outcomes.
  • Regulatory Compliance: Meets the requirements set by regulatory agencies, including the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA), helping avoid costly recalls and legal issues.
  • Product Quality and Consistency: Maintains consistent product quality, fostering trust and reliability in pharmaceutical products and medical devices.


Endotoxin testing is an indispensable part of the manufacturing process for pharmaceuticals and medical devices. By adhering to USP 85 requirements and employing robust testing methods, manufacturers can ensure that their products are safe for market release. As technology advances, so too does the sensitivity and efficiency of these testing methods, continuously enhancing patient safety and industry standards.

This comprehensive approach to understanding and implementing endotoxin testing underlines its crucial role in safeguarding public health and maintaining the integrity of pharmaceutical products and medical devices globally.

Do You Require Endotoxin Testing?

Contract Laboratory assists pharmaceutical and medical device companies with endotoxin testing through our network of qualified testing laboratories. If you need a lab Submit a Project Request, or Contact Us for more information.


  • Trevor Henderson BSc (HK), MSc, PhD (c), is the Creative Services Director for the Laboratory Products Group at LabX Media Group. He has more than three decades of experience in the fields of scientific and technical writing, editing, and creative content creation. With academic training in the areas of human biology, physical anthropology, and community health, he has a broad skill set of both laboratory and analytical skills. Since 2013, he has been working with LabX Media Group developing content solutions that engage and inform scientists and laboratorians.

    View all posts Director, Creative Services - LabX Media Group

Related Content


Editor's Choice