An improved in vitro pyrogen test: to detect picograms of endotoxin contamination in intravenous fluids using limulus amoebocyte lysate.

A method for in vitro pyrogen testing using Limulus amoebocyte lysate (LAL) has been described. The method is based upon the measurement of endotoxin-precipitable protein and can be used to measure picogram quantities equivalent to E. coli endotoxin in unknown solutions. When increasing concentrations of E. coli endotoxin are added to a constant amount of LAL and the reaction is allowed to proceed to completion, there is a proportional increase in the protein precipitated by endotoxin. Therefore, by measuring the amount of protein precipitated from LAL, it is possible to determine the equivalent E. coli endotoxin concentration in unknown solutions, when samples of the unknowns are run simultaneously with E. coli endotoxin standards and negative controls. The endotoxin proportional precipitation of protein occurs in reaction mixture showing gelation as well as in reaction mixture where the levels of endotoxin are lower than required for gelation. Determination of precipitated protein provides greater sensitivity for endotoxin detection than the gelation methods currently in use.