EU (endotoxin unit)

The unit of endotoxin activity, defined against the reference standard endotoxin (RSE). Because endotoxins from different bacteria vary in potency, measuring them by weight would be misleading, so activity units are used instead. Roughly, 1 EU corresponds to about 0.1–0.2 ng of reference endotoxin, but the exact relationship for a control standard endotoxin depends on the lysate lot and is stated on its certificate. Limits are written as EU/mL, EU/mg or EU per unit.