Endotoxin test (LAL test) for medical devices

Endotoxins (ancient Greek endo: "inside", "within", toxins, "the poisonous substance") are part of the outer cell mem­brane of gram-negative bacteria, which can lead to inflammation and other physiological reactions in the human body.

Endotoxins are lipopolysaccharides (LPS), i.e. compounds consisting of fat-like (lipo) components and sugar components (polysaccharides). During decomposition of the bacteria, parts of these are set free and have a toxic effect. These parts are referred to as endotoxins and, in contrast to other toxins, are not continually released by living bacteria into their en-vironment. They are extremely heat-stable and also survive conventional sterilization processes, i.e. even sterilized pro­ducts can have a high endotoxin load if they were heavily contaminated with bacteria prior to sterilization. These bacteria are killed in the process, releasing the endotoxins of the cell membrane.

The most sensitive method of endotoxin measurement is based on the use of the lysate of a certain cell typecalled ame­bocyte from the blood of the horseshoe crab (Limulus). The frequently used designation LAL test(limulus amebocyte ly­sate test) for testing for endotoxins also results from this. This lysate reacts on contact with endotoxins by agglutination.

Nowadays it is rather uncommon to test using the agglutination reaction. State-of-the-art technology uses the additional integration of industrial components which generate a color reaction when endotoxins are bonded which can then be measured quantitatively. The endotoxin concentration is specified in the unit EU (endotoxin units) per ml or per product.

Common limit values are 20 EU/product for products which do not come into contact with the central nervous system (CNS), 2.15 EU/product for products which come into contact with the CNS and 0.5 EU/product in eye surgery.

Test procedure

Extraction Extraction of the product in endotoxin-free water
Measurement Measurement of the endotoxin content of the extract
Analysis Calculation of the endotoxin load per product
Unit EU/ml - endotoxin units per milliliter, or EU per test object