Diagnostic markers for community-acquired pneumonia

Community-acquired pneumonia (CAP) is one of the respiratory infectious diseases caused by not only bacteria, but also viruses. Antibiotic agents are needed to treat only bacterial but not viral CAP. In addition, there are some non-infectious respiratory diseases in the differential diagnosis of CAP, such as malignant diseases, interstitial lung diseases, pulmonary edema, and pulmonary hemorrhage. We usually diagnose patients having CAP by comprehensive evaluation of symptoms, vital signs, laboratory examinations, and radiographic examinations. However, symptoms and vital signs are not specific for the diagnosis of CAP; therefore, we also use inflammatory biomarkers for differentiating bacterial from viral CAP and non-infectious respiratory diseases. We have used the white blood cell count, C-reactive protein (CRP), and erythrocyte sedimentation rate as common inflammatory biomarkers, but they are not specific for bacterial infection because they could be increased by malignant diseases and collagen diseases. Recently, some inflammatory biomarkers such as procalcitonin (PCT), soluble triggering receptor expressed on myeloid cells-1 (sTREM-1), pro-adrenomedullin (proADM), and presepsin have been developed as relatively specific biomarkers for bacterial infection. Many reports have evaluated the usefulness of PCT for diagnosing CAP. In this review, the characteristics of each biomarker are discussed based on previous studies.