Heparin enables the reliable detection of endotoxin in human serum samples using the Limulus amebocyte lysate assay.

The determination of lipopolysaccharide (endotoxin) in serum or plasma samples using Limulus amebocyte lysate (LAL)-based assays is currently not sufficiently reliable in clinical diagnostics due to numerous interfering factors that strongly reduce the recovery of LPS in clinical samples. The specific plasma components responsible for the endotoxin neutralizing capacity of human blood remain to be identified. There are indications that certain endotoxin-neutralizing proteins or peptides, which are part of the host defense peptides/proteins of the innate immune system may be responsible for this effect. Based on our finding that several antimicrobial peptides can be neutralized by the polyanion heparin, we developed a heparin-containing diluent for serum and plasma samples, which enables reliable quantification of LPS measurement in clinical samples using the LAL assay. In a preclinical study involving 40 donors, this improved protocol yielded an over eightfold increase in LPS recovery in serum samples, as compared to the standard protocol. This modified protocol of sample pretreatment could make LPS measurement a valuable tool in medical diagnostics.