Turbidimetric Assay Method or LAL Test

Endotoxins are naturally occurring toxins from the cell walls of Gram-negative bacteria. These toxins can cause a fever (pyrogen) response in humans if they are present in pharmaceutical products. This is why it is particularly important to test for the presence of these toxins in parenteral products and medical devices.

At Helvic we use the Limulus Amebocyte Lysate (LAL) tests to detect and quantify bacterial endotoxins extracted from the outer membrane of gram negative bacteria.

The critical component of the LAL reagents used in endotoxin tests is derived from blood cells (amebocytes) of the horseshoe crab, Limulus polyphemus. It contains the proteins of the blood clotting mechanism, which is triggered by endotoxins. This clotting reaction results in turbidity in the test solution directly proportional to the endotoxin concentration. A spectrophotometer is used to determine the turbidity and therefore the endotoxin concentration can be determined by specialised software.

LAL tests are described in the Bacterial Endotoxins Test chapter in the United States Pharmacopeia (Chapter <85>) and in the equivalent chapters in the European Pharmacopoeia (Chapter 2.6.14) and the Japanese Pharmacopoeia (General Tests, No. 4.01).

 

Gel Clot Method

Similar to the turbidimetric method the gel clot method is based upon the reaction between bacterial endotoxin and Limulus Amebocyte Lysate. This technique allows detection or quantification of endotoxins and is based on clotting of the lysate in the presence of endotoxins.

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