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 × 10(9) cells/l for endotoxaemic patients versus 10.8 ± 6.2 × 10(9) 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.