Endotoxins

Andersen Caledonia provides endotoxin testing at its Bellshill laboratory using the reference gel clot method. Endotoxin testing is used to check RO water, device implants and blood filters. Typical customers include device manufacturers, hospital sterile processing centres and dialysis centres.

Description of Test

These tests are performed on medical devices (typically implants) or water which may be injected directly or indirectly into the human blood stream or come into contact with spinal fluid. An endotoxin is a lipopolyscharride that comes from the cell membranes of gram negative bacteria. Bacteria release these endotoxins which are mainly made up of pyrogens (substances that induce fever) to provoke an immune response.

This testing is important as endotoxins can remain on devices such as endoscopes after sterilisation and so these tests are performed in accordance with HTM 2030 to investigate whether the levels of endotoxin present are high enough to be considered unsafe.

The test determines the level of endotoxins in the sample using the LAL (Limulus amebocyte lysate) gel clotting method. LAL is a very sensitive indicator of endotoxin and involves the specimen being incubated for 60 minutes at 37°C with a known sensitivity of limulus amebocyte lysate. The amebocytes (blood cells of horseshoe crab) contain proteins of blood clotting mechanism which are triggered by endotoxins. LAL reacts with bacterial endotoxins and the formation of a gel clot indicates that endotoxins are present.

A negative or no gel result is defined as the endotoxin content being less than the labelled sensitivity of the LAL reagent, and so the levels of endotoxin present are not high enough to produce a health risk. A positive or gel formation indicates that the level of endotoxins present may produce a substantial health risk.

For medical devices the level of endotoxins present must not exceed 20 Endotoxin units (EU) per device. For devices that come into contact with the cerebrospinal fluid the limit is 2.15 EU per device. Water used for dialysis has a limit of 0.25 EU/ml.