Elimination of false-positive limulus amebocyte lysate tests in patients with hyperlipidemia

Varying concentrations of lipopolysaccharide (LPS) and mannan suspensions were mixed with either saline or plasma from normal volunteers, heated to 100 degrees C for 10 min, and then subjected to the limulus amebocyte lysate test (LAL). A positive LAL in saline required minimum LPS and mannan concentrations of 10(-11) and 10(-5) g/ml, respectively, while the minimum concentrations premixed with plasma were 10(-13) and 10(-9) g/ml, respectively. Thus, use of plasma instead of saline increased assay sensitivity 100-fold for LPS and 10,000-fold for mannan. In the second part of the experiment, normal plasma was separated into lipid and nonlipid phases by Folch's method. LAL analysis of each phase revealed equal sensitivity for LPS and mannan in the nonlipid phase, but no sensitivity in the lipid extract. Subsequently, 200 ml of a fat emulsion (Intralipos) was administered to the normal volunteers, and LAL and lipid analyses were performed. The LAL turned positive in all volunteers. When LAL was positive, triglycerides (TG), chylomicron (Chyl), and very low-density lipoprotein (VLDL) increased significantly compared with when LAL was negative. It is concluded that plasma lipids increase the sensitivity of LAL and directly activate LAL when TG, Chyl, and VLDL concentrations are high. This effect of plasma lipids on LAL can be eliminated by extracting LPS and mannan in the nonlipid phase.