What are endotoxins, and why does sterility matter?

These are quality-control concepts for research materials. Endotoxins are lipopolysaccharides (LPS) from the cell walls of Gram-negative bacteria; they are heat-stable, so a product can be sterile (free of living microbes) yet still contain endotoxin — the two are different things and are tested separately. Sterility is assessed by culture methods (USP <71>); endotoxin by the LAL assay (USP <85>), which detects LPS down to very low levels (around 0.01 EU/mL). A COA addressing injectable-grade quality reports both. We describe these strictly as laboratory testing parameters — these compounds are not approved for human use, and this is not a statement that any product is safe to administer.