# What an Endotoxin Test Shows (and When It Actually Matters)

_An endotoxin test checks for bacterial byproducts that a purity (HPLC) test misses. Why the two are different and which peptides most need it. Educational only._

Source: https://growthguyscanada.coupons/articles/endotoxin-testing-peptides.html · Updated: July 11, 2026 · TorontoHealth — educational only, not medical advice.


> **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.

This builds on the basics in [how to read a peptide COA](/articles/how-to-read-a-peptide-coa.html) and [purity vs identity on a COA](/articles/coa-purity-vs-identity.html).

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_General educational information, not claims about any specific company. For research and educational purposes only. Not medical advice. Posts may contain affiliate links — the price you pay does not change._