Endotoxin (LAL) results on a peptide COA: units, limits and missing data

Why an endotoxin line matters in a laboratory file

The Bacterial Endotoxins Test detects or quantifies endotoxins from Gram-negative bacteria. [1] In the laboratory they matter because they can interfere with experiments. GenScript's peptide QC material notes that endotoxins are easily introduced during peptide production and that small concentrations can reduce cell viability or trigger immune responses in cellular assays. [4] For that reason some peptide manufacturers sell endotoxin analysis as an add-on test, separate from HPLC and mass spectrometry. [4] [5]

This guide is about reading and recording the result. It does not set or suggest any limit for use outside the laboratory.

Units: EU, EU/mg and the "less than" result

The harmonized chapter expresses endotoxin in Endotoxin Units (EU) and notes that one International Unit (IU) of endotoxin equals one EU. Reference standards are calibrated to the current WHO International Standard for Endotoxin. [1] Limits in pharmacopoeial monographs are written per unit of product, such as EU/mL, EU/mg or EU per unit of biological activity. [1] For a lyophilized peptide, EU/mg is the natural unit: endotoxin activity found, divided by the milligrams of material in the test solution.

Many results are reported as "less than" a value, for example "< 0.5 EU/mg". That figure is a reporting limit, not a measurement of zero. It depends on the test's sensitivity (lambda, the lysate's labeled sensitivity or the lowest standard-curve point) and on how concentrated the sample solution was. [1] Two certificates can both say "less than" and still differ tenfold in what they could have detected. Record the number and the units exactly as printed.

The three LAL techniques and the newer rFC method

The harmonized Bacterial Endotoxins Test uses amoebocyte lysate from horseshoe crabs and describes three techniques: gel-clot (clot formation), turbidimetric (turbidity after cleavage of an endogenous substrate) and chromogenic (colour after cleavage of a synthetic peptide-chromogen complex). Turbidimetric and chromogenic methods each come in end-point and kinetic forms. Any of the three can be used, and in doubt or dispute the gel-clot limit test decides. [1] ICH Q4B Annex 14 records that the European, Japanese and US pharmacopoeia texts are interchangeable in the ICH regions on those conditions. [2] FDA's question-and-answer guidance on pyrogen and endotoxin testing refers to USP chapter 85 and to gel-clot, photometric and kinetic methods. [3]

The April 2026 sign-off of Revision 2 adds a non-harmonised European Pharmacopoeia method G, a fluorimetric end-point method using recombinant factor C (rFC); the Japanese and US texts list no equivalent non-harmonised part. [1] If a certificate says "rFC", record that it is a different reagent system from LAL and note which pharmacopoeia text the laboratory cites.

Interference and glucans: what a careful report mentions

Samples can inhibit or enhance the reaction, which is why the chapter requires a test for interfering factors with spiked positive product controls, repeated when conditions change. Interference may be overcome by treatments such as filtration, neutralization, dialysis or heat treatment. [1] The chapter also notes that amoebocyte lysate reacts to some beta-glucans, and that glucan-blocking lysates exist. [1]

A detailed report will name the method, lysate sensitivity, dilution used and whether the positive product control recovered. A one-line result without these is still worth recording, but your file should note that interference controls were not shown.

Why research certificates often omit endotoxin

There is no single required endotoxin test for research-grade peptides. ICH Q4B Annex 14 says the evaluated pharmacopoeia texts contain no acceptance criteria and that limits should be specified in the application dossier unless an individual monograph sets them. [2] The harmonized chapter leaves product limits to individual monographs, written in units such as EU/mg, and a research reagent has no monograph. [1] So a supplier has no default limit to test against.

Supplier pages reflect this. Peptides EU, for instance, describes HPLC purity and mass spectrometry identity and does not mention endotoxin testing on the FAQ page we read. [6] Manufacturers that do offer it, such as GenScript and Bio-Synthesis, list it as a separate qualitative or quantitative assay. [4] [5] A missing endotoxin line is therefore normal for this market. It is still a gap if your assay is endotoxin-sensitive.

How to record it in the supplier file

If your work needs an endotoxin result the supplier cannot provide, the options are to ask for a quotation from the supplier for lot testing or to commission it yourself. Neither choice turns this guide into advice about use of the material outside the laboratory.

• Lot number, and confirmation that it matches the vial.
• Result exactly as printed, with units (EU/mg, EU/mL) and any "less than" sign.
• Technique (gel-clot, turbidimetric, chromogenic or rFC) and whether kinetic or end-point.
• Pharmacopoeia text cited (USP 85, Ph. Eur. 2.6.14 or JP 4.01) if stated.
• Testing laboratory and report number.
• Your own laboratory's specification, if one exists, and whether the reported value can be compared with it.
• Status: reported, reported without method, or not reported.