Measurement of endotoxin activity in critically ill patients using whole blood neutrophil dependent chemiluminescence

Background Lipopolysaccharide (endotoxin) from the cell wall of Gram-negative bacteria is a potent trigger for the release of host-derived inflammatory mediators. The relationship between endotoxaemia, Gram-negative infection and the clinical syndrome of sepsis has been difficult to establish, in part because of the limitations of available endotoxin assays. Methods We performed an observational cohort study in critically ill patients in the medical/surgical intensive care unit (ICU) of a tertiary care hospital. Whole blood endotoxin levels on the day of ICU admission were measured using a novel chemiluminescent assay – the endotoxin activity assay (EAA) – and the chromogenic modification of the limulus amoebocyte lysate (LAL) assay. Results We studied 74 consecutive admissions. Endotoxin levels were higher in patients with a diagnosis of sepsis (470 ± 57 pg/ml) than in patients admitted with a diagnosis other than sepsis (157 ± 140 pg/ml; P < 0.001). Endotoxaemia was significantly associated with Gram-negative infection (P < 0.05); no patient with a Gram-negative infection had an endotoxin level below 50 pg/ml. White blood cell counts of patients with EAA-detected endotoxaemia were significantly higher (15.7 ± 9.1 × 109 cells/l for endotoxaemic patients versus 10.8 ± 6.2 × 109 cells/l for patients without endotoxaemia; P < 0.05). Conclusion Endotoxaemia is associated with Gram-negative infection from any source, and with a diagnosis of sepsis and leukocytosis. These correlations were not apparent using the LAL method. The EAA may be a useful diagnostic tool for the investigation of invasive Gram-negative infection and incipient sepsis.

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