What is the most reliable marker in the differential diagnosis of pulmonary embolism and community-acquired pneumonia?

Because of similar clinical manifestations and laboratory findings, differential diagnosis of pulmonary embolism and community-acquired pneumonia (CAP) is generally difficult. Therefore, this study was conducted to find good markers for the easy, cheap, and fast differential diagnosis of pulmonary embolism and CAP. Thirty-four patients diagnosed with pulmonary embolism and 38 patients with CAP who were admitted to either emergency department or chest diseases outpatient clinic were included in this study. On admission and third day, complete blood count, C-reactive protein (CRP), erythrocyte sedimentation rate, procalcitonin (PCT), and D-dimer levels of each patient were measured. Neutrophil-to-lymphocyte ratio (NLR) was calculated using the formula NLR = neutrophil count/lymphocyte count. NLR/D-dimer and PCT/D-dimer ratios were also calculated. First day neutrophil count (P = 0.005), NLR (P = 0.002), CRP (P < 0.001), erythrocyte sedimentation rate (P < 0.001), PCT (P < 0.001), NLR/D-dimer (P < 0.001), and PCT/D-dimer (P < 0.001) levels were higher in patients with CAP compared with patients with pulmonary embolism. In stepwise logistic regression analysis done with all the parameters used for the differential diagnosis of pulmonary embolism and CAP, CRP, PCT/D-dimer, and NLR/D-dimer were found to be independent predictive factors for the presence of CAP. Among these factors, NLR/D-dimer ratio was found to be the most sensitive (97.4%) to have the highest negative predictive value 96.7% and to be the most accurate (area under curve = 0.921) (91.7%) parameter for the differential diagnosis of pulmonary embolism and CAP. In this study, NLR/D-dimer ratio was found to be more sensitive and more selective with negative predictive value and area under curve for the differential diagnosis of pulmonary embolism and CAP compared with other laboratory tests.