Sterility and Endotoxin Testing

Sterility and endotoxin are two separate quality questions that are easy to conflate. Both can appear on research-material documentation, and both describe the preparation — not how a material may be used.

Sterility: are viable microbes present?

A sterility assay (the compendial reference is USP <71>) asks whether viable microorganisms can be cultured from a sample. "Sterile" means none were detected under the test conditions. Sterility testing has well-known limitations: it samples a portion of a lot, so it reduces but never eliminates uncertainty.

Endotoxin: is bacterial residue present?

Endotoxins are heat-stable fragments of the outer membrane of Gram-negative bacteria. A material can be sterile (no living organisms) yet still contain endotoxin (residue left behind). The bacterial endotoxins test (USP <85>), often an LAL-based assay, quantifies that residue, typically in endotoxin units (EU).

How this shows up on a COA

• A line item for sterility with a pass/fail result and the method.
• A separate endotoxin result with a measured value and unit.
• The lot the tests were run against.

Because these are distinct assays, a thorough vendor reports them separately. Seeing one does not imply the other. As always, these results describe the research material itself and are not instructions for any use.