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Bacterial Endotoxin Test

Limulus Amebocyte Lysate TestThe Limulus Amebocyte Lysate (LAL), or bacterial endotoxin test, is an established pharmacopeial method (Ph. Eur, USP and JP) for the screening of parenteral medicines, irrigation fluids, dialysis solutions, and purified water. It is also used to assess the safety of medical devices designed to come into direct or indirect contact with blood and body tissues by testing for endotoxins via an extraction process used to flush material off the article ready for combining with LAL reagent.

The bacterial endotoxin testing has replaced the majority of rabbit in vivo pyrogen testing as lysate is both efficient and extremely sensitive, detecting very low levels of endotoxin even with repeated dilutions of the solution. The LAL test is based on an extract from the blood of the horseshoe crab (Limulus polyphemus), which has a primitive immune response clotting mechanism triggered by bacterial endotoxin present in the Gram negative bacterial cell wall.

Endotoxins will elicit a pyrogenic response and their presence is most likely the result of bacterial contamination at some point in the manufacturing process. These contaminants need not be viable; fragments of bacterial cell wall will give a febrile response.

We offer the following three standard methods for bacterial endotoxin testing:

Gel clot method

  • Reference method
  • Endpoint assay giving a positive or negative result at the sensitivity of the lysate used
  • Semi quantitative method; can be performed by preparing dilutions
  • Dilutions are tested with lysate and the endpoints used to calculate approximate endotoxin level

Kinetic chromogenic method

  • Lysate is formulated with a chromaphore which develops as the gel forms
  • Rate of development of colour from lysate is a measure of the amount of endotoxin in sample
  • As the gel does not have to completely form, this method has greater sensitivity
  • Sensitivity down to 0.005 EU/mL
  • Dilution enables the testing of products which may otherwise interfere with the system

Kinetic turbidimetric method

  • Similar to kinetic chromogenic method
  • Same sensitivity at 0.005 EU/mL
  • Measures turbidity via spectrophotometry rather than by colour development

For those products not suitable for the bacterial endotoxin test, we are pleased to now offer a new in vitro test method, the Monocyte Activation Test.  For more information on this test and other services, please visit the links below.