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Laboratory standards

Endotoxin testing

Why bacterial endotoxin is measured separately from microbiological contamination.

Bacterial endotoxins are lipopolysaccharide components of the outer membrane of Gram-negative bacteria. They are heat-stable and are not removed by processes that kill the organisms that produced them, which is why endotoxin is measured as a separate parameter rather than inferred from a microbiological result.

How it is measured

The established methods are based on the clotting cascade of horseshoe crab amoebocyte lysate, read by gel-clot, turbidimetric or chromogenic endpoint. Recombinant factor C assays provide an alternative that does not depend on animal-derived lysate. Results are expressed in endotoxin units per unit mass or volume.

As with every other test described in this section, a result describes the sample examined, at the time it was examined, by the method stated.

References