Limulus amebocyte lysate is a biochemical reagent extracted from the blue blood of limulus amebocyte lysate of marine arthropod and freeze-dried at low temperature, which is specially used for bacterial endotoxin detection. Limulus lysate is widely used to detect endotoxin in different samples such as food, water, medicines, medical devices and animal body fluids because it can react with bacterial endotoxin and β -glucan to form gel. The test using limulus reagent is called limulus test.

Horseshoe crab is a marine arthropod. There is a kind of nucleated deformed cell in its blood and lymph, and there are a lot of dense granules in its cytoplasm, which contain plasminogen and prothrombin. When endotoxin comes into contact with the lysate (lysate) of limulus amebocyte after freezing and thawing, it can activate plasminogen, and then turn soluble prothrombin into coagulated protein, so that the frozen-thawed lysate of limulus amebocyte is in a gel state.

A test to detect endotoxemia. Horseshoe crab is a kind of large arthropod living on the seashore, belonging to the class Araneae. The lysate of its multifunctional blood cells (deformed cells) contains a coagulable protein, which can form a gel in the presence of a very small amount of endotoxin (0.0005vg/ml). This experiment uses this principle to determine trace endotoxin in blood or other samples. In clinical cases, the positive rates of the following diseases are higher: endotoxic shock, acute suppurative cholangitis, severe hepatitis, peritonitis, liver cirrhosis and so on. About 2/3 of endotoxin positive cases lead to death.

According to the principle of limulus reagent reaction, it can be divided into qualitative limulus reagent and quantitative limulus reagent, and the corresponding tests are called qualitative limulus test and quantitative limulus test. Qualitative limulus test is mainly used for qualitative examination of endotoxin in drugs, medical devices and other products. Quantitative limulus test is mainly used to detect endotoxin in clinical patients and animals, and to provide reference for doctors to use drugs.