Abstract
BackgroundElevated blood endotoxin levels are frequently reported in the dialysis population and are strongly linked with inflammation, a major predictor of mortality. Virtually all studies have employed the Limulus Amoebocyte Lysate (LAL) assay to detect endotoxin. However this assay is not endotoxin-specific and can be activated by (1→3)-β-glucan (BG), a component of fungal cell walls leading to false positive signals. Very few studies have taken account of this. We examined the influence of BG-based activation of the LAL assay on the detection of endotoxemia in this setting.MethodWe measured plasma endotoxin levels in 50 hemodialysis patients with and without the use of BG-blocking buffers. These buffers inhibit BG activation of the LAL assay to ensure that any signal detected is endotoxin-specific. Blood samples were measured for BG, interleukin-6 (IL-6), tumor necrosis factor-alfa (TNF-α) to examine the association between endotoxin signals, BG and inflammation.ResultsEndotoxin signals were detected in 50% of patients. On repeat measurement with a BG-blocking buffer, all detected endotoxin signals were extinguished. No patient had detectable endotoxemia. Plasma BG levels were significantly elevated in 58% of patients and were higher in those with detectable endotoxin signals using the LAL assay without BG-blocking buffers (78vs.54pg/mL;p<0.001). Endotoxin signal and BG levels did not correlate with levels of TNF-α or IL-6.ConclusionUse of the LAL assay for blood endotoxin detection in dialysis patients has its limitations due to high blood BG. Endotoxemia frequently reported in non-infected hemodialysis patients may be artefactual due to BG interference.
Highlights
Endotoxemia is commonly reported in the dialysis population and has been associated with systemic inflammation[1,2,3,4,5,6,7]–a strong prognostic of poor outcome[8]
Plasma by (1!3)-β-glucan (BG) levels were significantly elevated in 58% of patients and were higher in those with detectable endotoxin signals using the Limulus Amoebocyte Lysate (LAL) assay without BGblocking buffers (78vs.54pg/mL;p
Use of the LAL assay for blood endotoxin detection in dialysis patients has its limitations due to high blood BG
Summary
Endotoxemia is commonly reported in the dialysis population and has been associated with systemic inflammation[1,2,3,4,5,6,7]–a strong prognostic of poor outcome[8]. The levels of endotoxemia reported in the dialysis population range from 0.209 to 2.31 endotoxin units/mL (EU/mL)[2], [3], [5], [7], [9,10,11,12] This appears high since it is well established that 4.1–5 EU/ kg/hr is sufficient to induce pyrogenic symptoms such as rigor, nausea and hypotension in humans [13], [14]. All studies have employed the Limulus Amoebocyte Lysate (LAL) assay to detect endotoxin. This assay is not endotoxin-specific and can be activated by (1!3)-β-glucan (BG), a component of fungal cell walls leading to false positive signals. We examined the influence of BG-based activation of the LAL assay on the detection of endotoxemia in this setting
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