CRP and bacterial infectious disease: PCT is a crucial biomarker for diagnosing bacterial infections and sepsis.[17] It can be activated by microbial toxins, interleukin-1, interleukin-6, and tumor necrosis factor-alpha.[18] When the body is infected by bacteria, serum PCT levels increase significantly, with higher concentrations correlating with more severe bacterial infections.[19] CRP is a nonspecific acute-phase protein synthesized by hepatocytes.