Endotoxin Testing Explained: What EU per Vial Means
What endotoxin is, how labs measure it with the LAL assay, what EU per vial means on a peptide COA, and how it differs from a microbial count.
What endotoxin is
Endotoxins are fragments of the outer membrane of certain bacteria (lipopolysaccharides). They are released when those bacteria die and break apart, and they survive conditions that kill the bacteria themselves.
That is why a product can be free of living bacteria and still carry endotoxin: it is a record of contamination at some point in manufacturing, not only of contamination now.
How it is measured
Most labs use the LAL (Limulus amebocyte lysate) assay, which reacts to endotoxin in a measurable way. The result is reported in EU, endotoxin units.
On a peptide COA it is normally given per vial, so a result of 1.5 EU/vial describes the whole vial. A result reported as below 1 EU/vial means the level was under what the assay measures at that range.
How to read the number
Lower is better. When comparing two reports, check they use the same unit (per vial, per mg or per mL), because the same material can look very different depending on which one is printed.
Endotoxin vs microbial testing
An endotoxin result and a microbial result answer different questions. The microbial panel (TAMC and TYMC) counts living bacteria, yeast and mould. The endotoxin assay measures bacterial fragments. A thorough COA reports both.
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