Procalcitonin (PCT) is a protein precursor of calcitonin that has been proposed to differentiate systemic inflammation of bacterial origin from viral. The lack of rise in viral infections may be due to virus stimulated production of interferon gamma by macrophages, which inhibits TNF-alfa in the immune response. Lower PCT levels have a 94% negative predictive value for bacterial co-infection in intensive care unit (ICU) for patients with confirmed influenza A [1].
