NEUTROPHIL CD11B EXPRESSION AS A DIAGNOSTIC MARKER FOR EARLY-ONSET NEONATAL INFECTION

Objectives: To determine whether neutrophil surface expression of CD11 b predicts early-onset infection or suspected infection in at-risk inf ants. Study design: CD11b expression on peripheral blood neutrophils w as' determined by flow cytometry of whole blood samples. Blood (0.1 ml ) was obtained from a convenience sample of at-risk infants admitted t o the neonatal intensive care unit, stained with antibodies detecting CD11b and CD15, chilled, and analyzed within 8 hours. Blood for cultur e, blood counts, and C-reactive protein (CRP) determination was obtain ed simultaneously. Subjects were grouped on the basis of culture resul ts and clinical signs, and investigators were blinded to CD11b level. Results: Of 106 subjects, seven had positive bacterial or viral cultur es (''confirmed infection''), 17 had clinical signs of infection but n egative cultures (''suspected infection''), and 82 had negative cultur es and no clinical signs (''no infection''). Neutrophil CD11b was elev ated in all infants with confirmed infection, 94% with suspected infec tion, and none with no infection. The negative and positive predictive values, sensitivity, and specificity were 100%, 99%, 96%, and 100%, r espectively, for diagnosis of neonatal infection at initial evaluation . CD11b levels correlated with peak CRP (r(2) = 0.76, p < 0.0001); how ever, CD11b was elevated at the time of admission in all five infants with proven bacterial infection, whereas CRP was normal until the seco nd day in the neonatal intensive care unit in three of these five. Bot h infants with positive viral cultures had elevated CD11b, but the CRP levels remained within normal limits. The negative predictive value o f neutrophil CD11b for identifying suspected or confirmed infection wa s 99%. Conclusion: This assay for neutrophil CD11b is a promising test for exclusion of early-onset neonatal infection. If validated prospec tively, this assay may reduce hospital and antibiotic use in the popul ation of neonates at risk for early-onset infection.