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Environmental Analysis

Endotoxin [ENDO]

Published: July 8th, 2009

Revised: March 3rd, 2023

Endotoxin is a lipopolysaccharide found in the cell membranes of Gram-negative bacteria. Endotoxin is a strongly proinflammatory material because of its interactions with receptors that stimulate the innate immune system. Exposure to endotoxin will initiate a strong inflammatory response in anyone and does not require allergic sensitization or individual sensitivity. Inhalation exposure to endotoxin is thought to be a contributor to a number of inflammatory airways diseases such as Farmer’s Lung Disease and other hypersensitivity pneumonitides.

Endotoxin exposures typically arise where fluids contaminated with Gram negative bacteria become nebulized, such as spray-mist type humidification systems, hot tubs. In industry, sewage treatment processes and synthetic and semisynthetic machining coolants are a common source of endotoxins.

This test measures endotoxin content of air (air samples for endotoxin must be collected using special endotoxin-free polycarbonate filter membranes), bulk or TefTex wipe samples using the Limulus Amoebocyte Lysate (LAL) assay. This sensitive bioassay measures endotoxin by a reaction that uses highly sensitive endotoxin recombinant receptors cloned from blood cells of the horseshoe crab (genus Limulus). This is the gold standard method of measuring endotoxin, and it is used in a wide range of applications including the testing of medical devices and pharmaceutical preparations.

We reported levels in endotoxin units (EU) per standard unit of material tested (e.g. EU/mg, EU/m³, etc.). This measure can be converted to gravimetric units (e.g., ng) if required. In the case of air samples, endotoxin levels in a test area are usually compared to background levels in a non-complaint area. Airborne endotoxin greater than 30 times above background has been suggested as an action-level (ACGIH 1999).

Laboratory code: ENDO

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