Community-acquired pneumonia (CAP) is common, and the delivery of optimum care to patients with CAP is important to limit the associated substantial mortality and morbidity. Although severity assessment of patients presenting with CAP using clinical scores such as the CURB65 (Confusion, Urea nitrogen, Respiratory rate, Blood pressure, 65 years of age and older) or Pneumonia Severity Index (PSI) scales aids management, there are many other areas in which the care of patients with CAP could be improved. For example, improved accuracy of identifying patients at risk of death (especially the significant proportion of deaths in patients with low clinical severity scores) or complications such as empyema would improve the stratification of patients for different intensities of management, and there are few data on how to decide the duration of antibiotic treatment for individual patients. Biomarkers may help with some of these questions, and in this month’s Thorax there are two articles (see pages 587 and pages 592 on the use of biomarkers in patients with CAP1 2 that join a series of often seemingly contradictory papers in this area published over the past few years. What are the main overall messages that can be concluded from the published research into biomarkers and CAP, and are their results convincing enough now to influence how patients with CAP are managed?

The National Institutes of Health definition of a biomarker is: “a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.” However, this definition would include clinical parameters such as temperature or respiratory rate, and in general a biomarker is given a narrower definition of a biochemical feature that can be used to diagnose or assess the progress of disease or the effects of treatment. As such, blood …