Supplementary Material for: Early Diagnosis of Intra-Abdominal Inflammation and Sepsis by Neutrophil CD64 Expression in Newborns

<p><i>Background:</i> Newborn infants with intra-abdominal inflammation/sepsis often present with nonspecific signs in the early stages of the disease, but can rapidly develop life-threatening complications. A reliable ‘early’ biomarker would be invaluable. <i>Objective:</i> To evaluate the effectiveness of neutrophil CD64 as an ‘early’ biomarker of intra-abdominal inflammation/sepsis. <i>Methods:</i> Blood was collected from newborns with suspected intra-abdominal pathology for neutrophil CD64 and C-reactive protein (CRP) determination at the onset of clinical presentation and 24 h later. They were classified into three groups: intra-abdominal inflammation/sepsis (group 1), extra-abdominal sepsis (group 2) and nonsepsis (group 3). Between-group comparisons were made by Kruskal-Wallis and χ<sup>2</sup> tests. Receiver-operating characteristic curves and diagnostic utilities for single and combination of tests were determined. <i>Results:</i> 310 infants were recruited (102, 34 and 174 in groups 1, 2 and 3, respectively). CD64 (conventional cutoff = 6,010 antibody-PE molecules bound/cell) had substantially better sensitivity (0.81 vs. 0.56) and negative predictive value (0.90 vs. 0.79) for diagnosing intra-abdominal sepsis than CRP, at presentation. Pairing CD64 with routine abdominal radiograph (AXR) substantially increased the sensitivity and negative predictive value for group 1 to 0.99 and 0.99, respectively. By adjusting the CD64 cutoff to 12,500 units, a substantial improvement in specificity could be achieved (0.62 to 0.80) without significantly compromising sensitivity (0.99 to 0.97). <i>Conclusions:</i> CD64 is a sensitive and ‘early’ biomarker for diagnosing intra-abdominal inflammation/sepsis. Intra-abdominal catastrophes, including necrotizing enterocolitis, intestinal necrosis, perforation and peritonitis can confidently be excluded using CD64 and AXR early in the course of the disease.</p>