Evaluation of Toxinometer ET-Mini and Endosafe-PTS endotoxin testing systems

Abstract

1914

Objectives: Toxinometer ET-Mini (Wako Chemicals USA, Inc.) and Endosafe-PTS (Charles River Laboratories) endotoxin testing systems were evaluated for sensitivity in limulus amoebecyte lysate (LAL) reagent water and diluted F-18 FDG (FDG), accuracy, ability to overcome the signal interference from an FDG solution, and general suitability for operation in the PET lab environment.

Methods: To determine the minimum detectable endotoxin concentration in LAL reagent water and FDG, test vials supplied by Wako Chemicals USA, Inc. and Endosafe-PTS cartridges were loaded with LAL reagent water or FDG (diluted 100-fold) containing increasing concentrations of United States Pharmacopoeia (USP) reference standard endotoxin (RSE) until endotoxin was detected in all replicates (n=5). To evaluate the accuracy of endotoxin detection over a range of endotoxin concentrations, vials and cartridges were loaded with LAL reagent water spiked to 0.05 (0.08 for PTS) , 0.5 and 1.0 EU/mL with RSE (n=5). For signal interference testing, FDG from three different synthesis units was tested (n=4) at 0, 10, 20, 40, and 100–fold dilutions. All samples were spiked to 0.3 EU/mL. LAL reagent water alone was used as a control in all studies.

Results: Toxinometer ET-Mini and Endosafe-PTS first detected endotoxin (in LAL water) at 0.05 and 0.08 EU/mL, respectively. FDG samples appeared to have no effect on the ability of Toxinometer ET-Mini to detect endotoxins when present at the level of stated sensitivity, while Endosafe-PTS showed a slight decrease in sensitivity (ranging from 0.11 to 0.13 EU/mL) while analyzing the same samples. Toxinometer ET-Mini detected 97 ± 5%, 76 ± 3%, and 69 ± 3% of the endotoxin concentration present for 0.05, 0.5, 1.0 EU/mL, respectively. Endosafe-PTS detected 104 ± 17%, 78 ± 11%, and 82 ± 14% of the endotoxin concentration present for 0.08, 0.5, 1.0 EU/mL, respectively. FDG samples recovered from signal interference at a 10-fold dilution (units 1 and 2) and 40-fold dilution (unit 3) for Toxinometer ET-Mini and 10-fold dilution (unit 1) and 20-fold dilution (units 2 and 3) for Endosafe-PTS.

Conclusions: The minimal detectable endotoxin concentrations in LAL water (sensitivity) for the tested Toxinometer ET-Mini and Endosafe-PTS systems are 0.05 and 0.08 EU/mL. The further decrease in sensitivity of Endosafe-PTS for 100-fold diluted FDG samples requires that the maximum valid dilution be recalculated. The accuracy is acceptable for both units in the tested range, considering the nature of the LAL reagent and the wide range specified by the USP for endotoxin detection accuracy. The measurements taken by Toxinometer ET-Mini were noticeably precise. The FDG formulation interferes with endotoxin testing in some cases until diluted 40-fold.