Home › Guides › What an Endotoxin Test Shows (and When It Actually Matters) By TorontoHealth Editorial · Updated July 11, 2026
What an Endotoxin Test Shows (and When It Actually Matters)
What does an endotoxin test on a peptide show? It checks for endotoxins — fragments left behind by bacteria — that a purity test (HPLC) does not detect. A peptide can read 99% pure for identity and still carry endotoxins, because the two tests measure completely different things. It matters most for peptides made biosynthetically.
Updated July 2026 · General educational information.
Why a purity number isn't the whole picture
Most COA discussion stops at "what's the purity percentage?" Here's what most people get wrong: purity (measured by HPLC) tells you how much of the sample is the target molecule versus other chemical junk. It does not look for biological contamination. Endotoxins are byproducts of bacteria, and they slip past a standard purity test entirely — so a clean HPLC number and an endotoxin problem can live in the same vial.
When does an endotoxin test actually matter?
Not equally for everything. The distinction is how the compound is manufactured. Peptides built by solid-phase chemical synthesis (like the GLP-1 class) are chemically assembled, so bacterial byproducts are less expected. But compounds made biosynthetically — grown using microorganisms because it's the cheaper route — are exactly where bacterial residue "might be expected." NAD+ is the textbook example of the biosynthetic route.
Test
What it answers
What it misses
Mass spec (identity)
Is this the right molecule?
How much is present, and contamination
HPLC (purity)
How much of the sample is the target?
Biological / bacterial contamination
Endotoxin
Are bacterial byproducts present?
Identity and chemical purity
How to use this when you read a COA
For chemically-synthesized peptides: identity + purity are the core checks; an endotoxin line is a bonus, not a dealbreaker.
For biosynthetic compounds like NAD+: an endotoxin result is the one extra test genuinely worth looking for.
Skip the scare tactics: heavy-metals testing is often marketed as a rigor signal but adds little for these compounds — it's mostly a talking point.
Remember the tests don't substitute: a great purity number never covers for a missing endotoxin check where one matters.