A recent publication in the Journal of Immunological Methods revisits a common problem with endotoxin detection in biological solutions. Using the Endosafe PTS (Charles River Laboratories) and the Kinetic-QCL LAL Assay (Lonza) with serum samples, they found that neither were accurate for determining endotoxin content due to the sequestration of endotoxin by serum proteins. Specifically, they found that this interaction caused an extended initial phase of the LAL reaction curve to the extent that a linear kinetic response was not established. The authors were not able to devise a heat/dilution protocol to overcome this sequestration. Additionally, they reported endotoxin contamination in several types of commonly used Vacutainer tubes.
BioDtech has also observed the significant issue of endotoxin neutralization by serum proteins and have developed the Endotoxin Sample Preparation (ESP™) kit to overcome this problem. ESP™ combines proper buffer conditions, heat and enzymatic digestion to allow accurate endotoxin detection in plasma and serum samples. The method has been used in human, mice, rat, rabbit and goat samples.