Comparison of Toxinometer ET-2000 and Toxinometer ET-Mini for bacterial endotoxin test on F-18 FDG

Abstract

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Objectives: The performance of Toxinometer ET-2000 and Toxinometer ET-Mini endotoxin testing units (Wako Chemicals USA, Inc.) were compared 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 (diluted 100-fold), test vials (Wako Chemicals USA, Inc.) were loaded with LAL reagent water or FDG 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 were loaded with LAL reagent water spiked to 0.05, 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-2000 and Toxinometer ET-Mini both detected endotoxins (in LAL water) at the stated sensitivity of 0.05 EU/mL. The FDG samples appeared to have no effect on the ability of Toxinometer ET-2000 or Toxinometer ET-Mini to measure endotoxin concentration at 0.05 EU/mL. Toxinometer ET-2000 detected 106 ± 6%, 97 ± 5%, and 87 ± 9% of the endotoxin concentration present for 0.05, 0.5, and 1.0 EU/mL, respectively. Toxinometer ET-Mini detected 97 ± 5%, 76 ± 3%, and 69 ± 3% of the endotoxin concentration present for 0.05, 0.5, and 1.0 EU/mL, respectively. FDG recovered from signal interference at a 20-fold dilution (units 1 and 2) and 40-fold dilution (unit 3) for Toxinometer ET-2000 and 10-fold dilution (units 1 and 2) and 40-fold dilution (unit 3) for Toxinometer ET-Mini system.

Conclusions: The minimal detectable endotoxin concentrations in LAL water (sensitivity) for the tested Toxinometer ET-2000 and Toxinometer ET-Mini systems were 0.05 EU/mL for both instruments, verifying the sensitivity stated by the manufacturer. FDG samples diluted 100-fold do not interfere with the sensitivity, causing no change in the maximum valid dilution calculation outlined in the USP. 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 both instruments were noticeably precise. The FDG formulation interfered with endotoxin testing on both units until diluted 40-fold in some cases.