PCSK1N and systemic inflammatory response syndrome: This study revealed that the concentrations of carnosine, citrulline, histidine, ornithine, proline, sarcosine, threonine, tryptophan, tyrosine, valine, isoleucine, cystathionine, lysine, anserine, phosphoethanolamine, asparagine, leucine, BCAAs, and SAAs, as well as the BCAA/AAA ratio, were lower in the SIRS and sepsis groups, but the serum levels of arginine, glutamine, phenylalanine, taurine, aspartic acid, ethanolamine, homocitrulline, and glutamic acid were higher in these groups.