How is endotoxin tested?

The limulus amebocyte lysate assay (LAL assay) is the most used method for endotoxin testing. LAL is an aqueous extract of blood cells from horseshoe crab. It reacts with endotoxin in a system of cascade, with multiple enzymes working in sequence to produce detectable signals. Three forms of LAL assay are currently available in market: gel-clot, turbidimetric, and optical (including colorimetric and fluorometric) assays.