h Although tuberculosis (TB) is a reemerging disease that affects people in developing countries and immunocompromised populations in developed countries, the current diagnostic methods are far from optimal. Metabolomics is increasingly being used for studies on infectious diseases. We performed metabolome profiling of plasma samples to identify potential biomarkers for diagnosing TB. We compared the plasma metabolome profiles of TB patients (n ؍ 46) with those of community-acquired pneumonia (CAP) patients (n ؍ 30) and controls without active infection (n ؍ 30) using ultrahigh-performance liquid chromatographyelectrospray ionization-quadrupole time of flight mass spectrometry (UHPLC-ESI-QTOFMS). Using multivariate and univariate analyses, four metabolites, 12R-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid [12(R)-HETE], ceramide (d18:1/16:0), cholesterol sulfate, and 4␣-formyl-4-methyl-5␣-cholesta-8-en-3-ol, were identified and found to have significantly higher levels in TB patients than those in CAP patients and controls. In a comparison of TB patients and controls, the four metabolites demonstrated area under the receiver operating characteristic curve ( T uberculosis (TB) is a disease caused by the bacterium Mycobacterium tuberculosis. Although it is a well-known disease that has been around for much of human history, there are still millions of new TB cases occurring per year worldwide, and TB remains a leading cause of deaths worldwide, especially in developing countries. Since the 1980s, TB has reemerged as a result of the AIDS epidemic and increasing use of immunosuppressants. In recent years, a higher incidence of extrapulmonary disease in immunocompromised hosts and the emergence of multidrug-resistant strains have further complicated diagnosis and treatment (1-3). Despite the medical importance of TB, diagnosis is still associated with many unresolved problems. The traditional gold standard methods are smear and culture for acid-fast bacilli from clinical specimens. Although culture offers higher sensitivity and specificity than those of smears, it is not useful for culture-negative cases, especially in early, disseminated, or extrapulmonary disease (4, 5). Moreover, it often takes 2 to 6 weeks before culture is positive and even longer for definitive species identification. While newer diagnostic modalities, such as adenosine deaminase levels in pleural fluid, lipoarabinomannan levels in urine, PCR, and Xpert MTB/RIF assays, have been developed (6-12), there are still limitations in terms of their sensitivity and/or specificity.Metabolomics is an emerging platform for studies of infectious diseases or pathogens (13)(14)(15)(16)(17)(18)(19). For TB, the technique has been applied on cultured isolates for differentiation from other Mycobacterium species and studies on the biology and virulence of tuberculosis (14,15,(20)(21)(22). For example, lipidomics studies have revealed novel metabolites potentially associated with growth and virulence of M. tuberculosis (23,24). We also recently identified ...