Procalcitonin is a peptide released by human cells in response to exposure to bacterial toxins and is measurable in the serum. Procalcitonin is also downregulated in the setting of viral infection. Therefore, it is more specific than CRP or white blood cell count. Procalcitonin has been studied as a marker to determine both when to start antibiotic therapy and duration of antibiotic therapy in infection. In these trials, antibiotics were safely held or withdrawn when the procalcitonin level was normal or decreasing by a substantial amount. Systematic reviews of available literature support the use of procalcitonin to guide treatment in patients presenting with acute respiratory infections and sepsis. Antibiotic consumption is significantly reduced across different clinical settings when guided by procalcitonin levels; procalcitonin can be used effectively in these settings only when used as a point of care test.