Excerpt taken from: http://www.horseshoecrab.org/med/med.html
How is an LAL test performed?
To use the commercial product, a laboratory reconstitutes the vial of freeze-dried LAL with endotoxin-free water. An equal amount of reconstituted LAL, usually 0.1 ml, is then added to the sample solution in a small, glass, endotoxin-free test tube. The mixture is then incubated at 37C for one hour. At the end of this time, the mixture is examined for gel formation by gently inverting the tube. If sufficient endotoxin was present in the sample, a firm gel, one that can withstand inversion of the tube, is formed. Knowing the sensitivity of the LAL then allows the investigator to determine the quantity of endotoxin in the sample. If the sample is found to contain an amount that exceeds the limit set by the FDA, the sample fails and the lot of pharmaceutical product must be rejected. The US FDA currently requires the LAL test to be performed on all human and animal injectables as well as medical devices used to deliver these injectables. In addition, many implantable devices and artificial kidneys used for renal dialysis also require an LAL test.
Are there other uses for LAL?
Since LAL detects endotoxin, a component of Gram-negative bacteria, the test can also be used to detect the presence of these bacteria. However, there are two major drawbacks:
1. LAL cannot discriminate between living and dead bacteria, and
2. LAL cannot differentiate species of bacteria-endotoxin, which cause a similar reaction with LAL.
Even with these drawbacks, the LAL test has been used to rapidly diagnose urinary tract infections and spinal meningitis. In these cases, the presence of endotoxin is almost always indicative of living bacteria, i.e., an infection, and the types of bacteria causing these infections are few and quite similar. The LAL test has also been used to assess food spoilage (fish, milk, ground beef), air and water quality, and (in experiments) to determine the ability of new drugs to neutralize the toxic effects of endotoxin.
Are there other compounds in the horseshoe crab that are of biomedical interest?
Besides LAL, a number of reagents and medically useful compounds have been discovered in the blood of the horseshoe crab. These include:
- A new test for fungal infections (G-Test) which is already in use in Japan and is expected to be licensed in the US next year
- An endotoxin-neutralizing protein which has potential as an antibiotic as well as an alternative endotoxin assay. This protein, ENP, can be made synthetically, which would eliminate the use of live horseshoe crabs for the LAL reagent.
- A number of other proteins that show anti-viral and anti-cancer activity.
Written for ERDG by: Thomas J. Novitsky, Ph.D.
Edited by: Lisa Smith