Endotoxin LAL Testing 

Endotoxins are potentially toxic natural compounds of the cell wall of gram negative bacteria. This material is pryrogenic meaning that it can cause high fevers in humans. The test for Bacterial Endotoxin is used to detect or quantify endotoxins using Limulus Amoebocyte Lysate (LAL) which is an extract of blood cells from the horseshoe crab (Limulus polyphemus).

Two methods for Endotoxin Testing within parenteral preparations and medical devices can be performed at ILS:


 Gel Clot Method (Method A) LAL



 Turbidemetric Kinetic Method (Method C) LAL




Gel Clot Method (Method A) LAL Testing

The gel clot method is based upon the reaction between bacterial endotoxin and a specific lysate. This particular lysate is derived from the circulating amebocytes associated with the blood-clotting mechanism of the horseshoe crab Limulus polyphemus. (LAL)

If a gel is formed via a clotting reaction, endotoxin is present and the sample fails the test.

Turbidimetric Kinetic Method (Method C) LAL Testing

Turbidity testing determines the cloudiness of a solution by measuring the loss of intensity in a light beam passing through that solution. The cloudiness is caused as the insoluble coagulin concentration increases.

A mixture of the test substance is produced along with the LAL this solution is then illuminated by a spectrophotometer. If a clotting reaction has occurred the solution will become cloudy. The turbidity is proportional to the endotoxin concentration. Specific software is used to measure and analyse the data to determine the onset of turbidity. A fixed threshold is used and its value decreases with higher endotoxin concentration.


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