Delta neutrophil index as a marker for differential diagnosis between flare and infection in febrile systemic lupus erythematosus patients.

Fever is a common symptom of systemic lupus erythematosus (SLE), and because of this it is difficult to discriminate between SLE flare and infection. The delta neutrophil index (DNI), automatically determined by the ADVIA 2120 electronic cell analyzer, has been reported to reflect the fraction of circulating immature granulocytes and to be associated with the presence of infection. In this study, we investigated the utility of DNI in discriminating infections from SLE flares in febrile SLE patients. In total, 111 episodes in 92 febrile SLE patients were reviewed. The infection group showed significantly higher white blood cell counts, neutrophil counts, C-reactive protein and procalcitonin than the SLE flare group. Complement (C)3 and C4 levels were decreased significantly in the SLE flare group. Patients in the SLE flare group had significantly lower DNI than those in both infection groups, with or without bacteremia. In a multivariate logistic regression analysis, only DNI was a significant independent factor for the presence of infection (odds ratio (OR): 18.9). When we selected a DNI value of 2.8% as the cutoff for infection, SLE patients with DNI ≥ 2.8% were found to be at higher risk for infection than those with DNI <2.8% (relative risk 8.48-fold). Our data suggest that DNI may be a marker to differentiate infections from SLE flares in febrile SLE patients.