Chromogenic assay of endotoxin in platelet poor or rich plasma

In order to determine which sample preparation, platelet rich plasma (PRP) or platelet poor plasma (PPP), is more suitable for clinical endotoxin assay, we investigated the binding of endotoxins to platelets by comparing the amount of endotoxin in PRP with that in PPP, using a newly developed colorimetric assay with chromogenic substrate (Boc-Leu-Gly-Arg-pNA). When purified endotoxins were added to human whole blood, the amount of endotoxin recovered in PPP was significantly lower than that in PRP for all endotoxins tested except that from E. coli 0111:B4 and their ability to bind to platelets was varied depending on the species of bacteria from which they were purified. However, the amount of endotoxin in PRP obtained from surgical patients (n = 50) was almost same as that in PPP with a correlation coefficient r = 0.95, indicating that natural endotoxins circulating in human blood may not bind to platelets and that PPP can be used for endotoxin assay as well as PRP.