Introduction to the LAL Test

 

Limulus Amebocyte Lysate (LAL) tests 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. LAL reagents are primarily used to test for endotoxins in injectable pharmaceuticals, biological products, and medical devices. They are also used in renal dialysis centers and a wide range of other applications.

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CRL ENDOSAFER LAL Test Methods

There are three principal LAL test methods: the gel-clot, turbidimetric and chromogenic methods. The latter two may be grouped together as photometric methods as they require an optical reader.

 

Gel-clot Method

This is the simplest LAL test. The formation of a gel-clot indicates the presence of endotoxin in a sample. The method is performed in small test tubes and is read manually by inverting the test tubes. The maximum sensitivity is 0.015 EU/mL.

 

 

Turbidimetric Method

The optical density (turbidity) increase that accompanies the clotting reaction is read at 340 nm, in a incubating microplate reader. The maximum sensitivity of 0.001 EU/mL can be achieved.

 

 

 

Chromogenic Method

The LAL reagent is formulated with a synthetic substrate which produces a chromophore when cleaved by endotoxin activated enzyme. The test is read at 405 nm, usually in a microplate reader. The maximum sensitivity of 0.005 EU/mL can be achieved.