Bacterial endotoxin testing
Quantifying bacterial endotoxin, which is a separate question from chemical purity.
Purpose
Quantifying bacterial endotoxin, which is a separate question from chemical purity.
This page exists so that a discussion about a number can start from a shared understanding of what produced it. It is written for a reader who is technically literate but not a practising analyst.
How it works
Endotoxin is lipopolysaccharide from Gram-negative bacterial cell walls. It is pyrogenic, it is not removed by sterile filtration, and it is invisible to a chromatographic purity assay. A chemically pure preparation can carry a clinically significant endotoxin load.
The classical method is the limulus amoebocyte lysate assay, in gel-clot, turbidimetric or chromogenic formats. Recombinant factor C assays are an animal-free alternative with equivalent performance for most purposes.
What determines the result
Endotoxin limits for parenteral preparations are expressed per dose and per kilogram of body weight, which means a limit is meaningless without knowing the intended dose. A certificate that reports an endotoxin figure without units and a basis has not told you much.
Typical criteria
| Parameter | Typical value or criterion |
|---|---|
| Methods | LAL gel-clot, turbidimetric, chromogenic; recombinant factor C |
| Units | Endotoxin units per mg or per mL, referenced to a dose |
| Not covered by | Chromatographic purity, sterility testing, or mass spectrometry |
These are typical values, not universal standards. The criteria that apply to a specific result are the ones in the validated method that produced it, which is why a report without a method identifier is harder to interpret than one with.
What it cannot tell you
Every analytical method answers one question. The most common error in this community's discussions is treating an answer to one question as an answer to another: a mass match read as a purity result, a purity figure read as a content determination, a sterility test read as a guarantee of safety.
When you read a report, write down which question was asked. The rest follows.
Related pages
Other method notes in this commons cover the neighbouring techniques, and the certificate interpretation page covers how these results get reported. The impurities subcategory is where the discussion happens.
Revision history
| 2026-06-19 | Birkeland | Restructured into shorter sections so the outline navigation is usable. |
| 2026-03-14 | trough_index | Corrected a unit label in the second table — it read mg where it should have read mg/mL. |
| 2025-10-26 | s.chowdhury | Annual review: checked every figure against its source. Two rounded values tightened. |
| 2025-09-16 | y.mensah | Updated a dated claim and added the date explicitly, per the maintenance convention. |
| 2025-06-26 | forest_plot | Citation sweep: two references did not support the sentences attached to them and have been replaced. |
| 2025-03-07 | o.lindgren | Recorded a dissent from one maintainer rather than resolving it silently. |
| 2025-02-10 | bench_notes | Initial promotion from the source topic. Structure taken from the marked solution. |
Every edit to a maintained document records its author and a note explaining the change. An edit without a note may be reverted by any wiki editor under R9, and the revert is logged. Disagreements about content belong on the source topic rather than in the revision history (R10).
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