Dextran sulfate restores endotoxin detectability in human serum

Accurate quantification of endotoxins in human serum is essential for both clinical diagnostics and biomedical research but is frequently compromised by low endotoxin recovery (LER) in Limulus amebocyte lysate (LAL) assays. Here, we systematically evaluated natural and synthetic polyanions as additives to neutralize HDPs and restore LAL-detectable endotoxin activity in human serum. Dextran sulfate, polyacrylic acid, fondaparinux, enoxaparin, and chondroitin sulfate were screened using complementary bacterial growth assays and kinetic chromogenic LAL measurements. Among all tested compounds, dextran sulfate (DS40) showed the highest efficacy in neutralizing serum-derived HDPs. At an optimized concentration of 0.06 mg/mL, DS40 consistently restored endotoxin recovery within pharmacopeial acceptance criteria (50-200%) for purified and naturally occurring endotoxins derived from Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Performance was comparable to unfractionated heparin, a previously established HDP-neutralizing additive. Importantly, DS40 did not interfere with assay linearity or sensitivity and fully complied with European Pharmacopoeia requirements for the absence of interfering factors. Compared to heparin, DS40 offers superior batch-to-batch consistency, lower cost, improved sustainability, and eliminates the use of animal-derived components. These findings establish DS40 as a robust, chemically defined additive for overcoming LER and enabling reliable endotoxin quantification in human serum, thereby improving the analytical performance of LAL-based assays.