Use of Delta Neutrophil Index for Differentiating Low-Grade Community-Acquired Pneumonia From Upper Respiratory Infection

Dear Editor Pneumonia is a major cause of death worldwide, especially in aging and immunodeficient patients [1]. Common symptoms such as cough, fever, dyspnea, chest pain, and wheezes occur not only in pneumonia but also in many other illnesses. Early diagnosis of pneumonia is crucial, especially when symptoms are mild, to avoid overuse of antibiotics and prevent development of antibiotic resistance [2]. Therefore, rapid biomarkers are required to assist the initial evaluation and differentiation of lowgrade pneumonia from upper respiratory infection (URI). The delta neutrophil index (DNI), an automated hematology analyzer-based marker, was recently introduced. DNI is the fraction of immature granulocytes identified automatically by the ADVIA 2120i Hematology Analyzer (Siemens Healthcare Diagnostics Inc., Erlangen, Germany). DNI is associated with the diagnosis and prognosis of sepsis [3, 4]. In this study, we evaluated the diagnostic power of DNI for the differentiation of lowgrade community acquired pneumonia (CAP) from URI in patients with clinically ambiguous symptoms. After obtaining approval from the institutional review board (IRB) of the Catholic Medical Center (IRB number: UC12SISI 0087), we recruited 127 patients (mean age±SD 58.3±24.2 yr, Table 1A) for the study, which was carried out from September 2013 through November 2013. The inclusion criterion for patients with low-grade CAP was low severity, according to the CURB-65 system (score 0 or 1) [5]. URI (known as the common cold) was defined as a typical acute infection involving the nose, paranasal sinuses, pharynx, larynx, and trachea without radiographic findings of pulmonary infiltrate. Patients without infection were used as the control group. Total and differential leukocyte counts and DNI values were obtained with an ADVIA 2120i system. DNI was calculated with the following formula: DNI (%)=(neutrophil %+eosinophil % measured in the myeloperoxidase [MPO] channel with the cytochemical MPO reaction)-(polymorphonuclear neutrophil % measured in the nuclear lobularity channel). The level of C-reactive protein (CRP) was measured with a Hitachi 7600 Modular Chemistry Analyzer (Hitachi, Tokyo, Japan). Sputum and blood microbial cultures were performed before the start of antibiotic therapy. Among the 22 total isolates, the main CAP isolates were Staphylococcus aureus (n=9), Acinetobacter baumannii (n=4), Klebsiella pneumoniae (n=3), and Streptococcus pneumoniae (n=2). Bacteremia was found in two of 59 (3.4%) CAP patients and was not found in the URI and control groups. All of the pa-