Endotoxin, sterility and heavy metals: what the extra tests cover
By BioGenisys Research Team · 4 min read · Updated 2026-10-27
Identity and purity are the core of a peptide lab report. Some reports go further and test for bacterial toxins, live germs and heavy metals. Not every report includes these, and a missing test doesn't mean something is wrong, but it helps to know what each one checks.
The short version
- Endotoxin: leftover bits of bacteria. Lower is better.
- Sterility: whether any live germs grow from the sample. Pass or fail.
- Heavy metals: tiny traces of metals such as lead. Each should be under its limit.
Endotoxin (the LAL test)
Endotoxins are bits of the outer shell of certain bacteria. They can stay behind even after the bacteria themselves are dead, so a sample can be germ-free and still contain endotoxin. In lab experiments on cells, endotoxin can set off strong reactions in some cell types and throw off results that have nothing to do with the compound being studied.
The standard test uses an extract of horseshoe crab blood, called LAL (short for Limulus amebocyte lysate), which reacts to endotoxin. Results are given in endotoxin units (EU), usually per milligram of compound, for example below 1 EU/mg. Lower is better.
Sterility
A sterility test checks for live germs. The lab puts some of the sample into a nutrient broth and watches whether anything grows, usually for 14 days. The result is pass or fail. Because it takes about two weeks, it isn't run on every batch.
Heavy metals
Tiny traces of metals can get in during manufacturing or from equipment. A very sensitive instrument called ICP-MS can detect metals such as lead, arsenic, cadmium and mercury down to parts per million (ppm) or less. One part per million is about one drop in a 13-gallon barrel. Results are given for each metal or as a total, against a stated limit.
How to read them
| Test | How the result is shown | What a good result looks like |
|---|---|---|
| Endotoxin (LAL) | EU per mg | Under the stated limit, for example below 1 EU/mg |
| Sterility | Pass or fail | Pass, with the test method named |
| Heavy metals (ICP-MS) | Parts per million (ppm), per metal or total | Each metal under its stated limit |
Like everything else on a report, each test applies only to the batch that was tested. See How to read a peptide lab report for the rest.
For research use only. Not for human or veterinary use.