Comparison of lipopolysaccharides and soluble CD14 measurement between clinically endotoxaemic and nonendotoxaemic horses

Reasons for performing study: Clinically useful biomarkers are needed for early identification of endotoxaemic horses. Soluble CD14 (sCD14) is amplified early in response to inflammatory signals, including bacterial lipopolysaccharide (LPS), and may prove a useful biomarker for clinical endotoxaemia. Objectives: The aim of this study was to determine if sCD14 could serve as a more reliable biomarker of the clinical signs of endotoxaemia, compared to measuring LPS alone. Study design: Prospective observational study in horses at a veterinary teaching hospital. Methods: Plasma samples were collected from 20 healthy horses and 35 horses presenting for emergency evaluation. Horses were classified as clinically endotoxaemic, using previously established criteria, if they had a heart rate >70 beats/min, packed cell volume >45% and/or a lesion likely to result in endotoxaemia. Soluble CD14 was measured using a cytometric bead-based assay and LPS was measured using a Limulus amoebocyte lysate (LAL) assay. Results: Soluble CD14 was higher in horses classified as clinically endotoxaemic (median 1102 ng/ml, interquartile range 439 ng/ml), compared to clinically nonendotoxaemic (median 692 ng/ml, interquartile range 455 ng/ml, P = 0.03. There was no difference in LPS concentrations between clinically nonendotoxaemic (median 5.4 endotoxin units [ EU]/ml, interquartile range 5 EU/ml) and endotoxaemic horses (median 7.2 EU/ml, interquartile range 17 EU/ml, P = 0.2). There was no correlation between sCD14 and LPS values in paired serum samples. LPS and sCD14 values were used to generate a receiver operating characteristic curve. The area under the curve for LPS and sCD14 was <0.7, suggesting that sCD14 and LPS were poor predictors of clinical endotoxaemia for the horses in this study. Conclusions: Further investigation is warranted to assess the utility of sCD14 measurement as a clinically useful biomarker to identify endotoxaemia in horses.