Interleukin 6 in neonates with early and late onset infection.

Objective: To assess the utility of determining interleukin 6 (IL-6) concentrations for diagnosing early (< or = 48 h of life) and late onset infection in a neonatal intensive care setting.

Methods: We measured serum IL-6 values in five groups of neonates on both postnatal Days 1 and 2 (early sampling): Group 1, patients with clinical and microbiologic evidence of early onset infection; Group 2, patients with negative body fluid cultures but strong evidence of infection (clinical septicemia); Group 3, patients without clinical and microbiologic evidence of infection; Group 4, patients in whom infection could be neither confirmed nor excluded; and Group 5, healthy neonates with a normal postnatal course. We also measured IL-6 values in older neonates who during their hospital stay developed systemic infection (late sampling). Three controls matched for duration of hospital stay and birth date were chosen for each patient.

Results: On postnatal Day 1 IL-6 values were elevated in all four patient groups compared with those in healthy neonates (P < 0.05 by analysis of variance (ANOVA)). There were no significant differences found among patient groups. On postnatal Day 2 IL-6 concentrations were persistently elevated in Groups 1 and 2 compared with values from those in Group 3, Group 4 and healthy controls (P < 0.01). At this time no significant differences in IL-6 values were found between uninfected symptomatic patients (Group 3), patients with uncertain findings (Group 4) and healthy controls. IL-6 concentrations were significantly higher in patients with late onset infection at presentation than in the patient controls (P < 0.0001) and returned to low values in those who recovered from infection.

Conclusions: There are differences in the serum concentrations of IL-6 that can be helpful in detecting early and late onset infection in preterm and term neonates. During the first 48 h of life serial IL-6 determinations are necessary so as not to overdiagnose infection in a neonatal intensive care setting.