As the proverb says, blood is thicker than water, and in endotoxin testing, you can take this literally. Unlike water, blood-based samples contain many components interfering with endotoxin detection assays, making them one of the most difficult sample types to test. Whole blood is highly interfering, so often serum or plasma is used instead.
Blood proteins like albumin are widely-known interference factors which may mask any endotoxin contained in the sample. To free the endotoxin bound to these proteins, as well as inactivate any proteases that may be present, a heat treatment may be performed. Make sure to include a “hard” spike (i.e. add a known amount of endotoxin before the heat treatment), so you can show the treatment doesn’t lead to an endotoxin loss. Alternatively, you can add a dispersing agent like PYROSPERSETM Dispersing Agent to counteract endotoxin masking.
Another potential interfering factor are anticoagulants (e.g. heparin) that may be present in your blood preparation. They are used to prevent the blood from clotting, but unfortunately, they also interfere with the LAL enzymes. Anticoagulants act as chelators, binding divalent cations that are necessary for the LAL enzymes to function. Adding MgCl2 solution can overcome this problem.
For more tips regarding endotoxin testing of blood-based samples, download our TechTip “Serum/Plasma Testing with PYROGENTTM-5000 and Kinetic-QCLTM Assays” from the QC InsiderTM Portal.
Written by Saskia
Scientific Support Specialist, Lonza Pharma-Bioscience Solutions at Lonza