Inoue S, et al. - In patients with acute exacerbation of COPD (AECOPD), researchers examined amino acid levels. Blood was collected from AECOPD hospitalized patients and COPD patients in stable condition. Investigators found that plasma amino acid levels differ in AECOPD patients depending on whether bacterial infection occurs or not. They suggested that specific amino acids (ie, asparagine, citrulline, glutamine, histidine, serine, and threonine) may serve as diagnostic markers for distinguishing between bacterial and nonbacterial AECOPD.