Role of the Neutrophil-Lymphocyte Count Ratio in the Differential Diagnosis between Pulmonary Tuberculosis and Bacterial Community-Acquired Pneumonia

BACKGROUND Differential diagnosis between pulmonary tuberculosis (TB) and bacterial community-acquired pneumonia (CAP) is often challenging. The neutrophil-lymphocyte count ratio (NLR), a convenient marker of inflammation, has been demonstrated to be a useful biomarker for predicting bacteremia. We investigated the usefulness of the NLR for discriminating pulmonary TB from bacterial CAP in an intermediate TB-burden country. METHODS We retrospectively analyzed the clinical and laboratory characteristics of 206 patients suspected of having pulmonary TB or bacterial CAP from January 2009 to February 2011. The diagnostic ability of the NLR for differential diagnosis was evaluated and compared with that of C-reactive protein. RESULTS Serum NLR levels were significantly lower in patients with pulmonary TB than in patients with bacterial CAP (3.67±2.12 vs. 14.64±9.72, P<0.001). A NLR <7 was an optimal cut-off value to discriminate patients with pulmonary TB from patients with bacterial CAP (sensitivity 91.1%, specificity 81.9%, positive predictive value 85.7%, negative predictive value 88.5%). The area under the curve for the NLR (0.95, 95% confidence interval [CI], 0.91-0.98) was significantly greater than that of C-reactive protein (0.83, 95% CI, 0.76-0.88; P=0.0015). CONCLUSIONS The NLR obtained at the initial diagnostic stage is a useful laboratory marker to discriminate patients with pulmonary TB from patients with bacterial CAP in an intermediate TB-burden country.