Objective To observe the clinical effect of calcitonin(PCT) in the identification of bacterial infection and viral infection.Methods 150 cases were randomly selected,including 50 cases of viral infection,100 cases of bacterial infection.The people with physical examination at the same period in the hospital whose peripheral blood culture were negative were selected as control group.PCT concentrations of various bacterial infections were observed,as well as the concentrations of PCT in various viral infections,and compared with the control group.Results The PCT level in the bacterial infection group was (8.023±3.542)ng/mL, which was significantly higher than (0.031±0.011)ng/mL in the control group(t=15.960,P=0.000).There was no significant difference in the level of PCT between the viral infection group [(0.032±0.008)ng/mL] and the control group [(0.031±0.011) ng/mL] (t=1.903,P=0.059).In different bacterial infections,the PCT level in sepsis was the highest [(17.544±4.511)ng/mL],followed by bacterial peritonitis and infectious pancreatitis[(5.131±1.231)ng/mL,(4.941±1.665)ng/mL].The PCT level of cellulitis was the lowest [(27.544±4.511)ng/mL].Of a variety of viral infections,the patients with EB virus infection had slightly higher PCT level[(0.027±0.002)ng/mL],which of measles virus infection was slightly lower[(0.021±0.002)ng/mL],the overall PCT level had no significant difference.Conclusion It is important to identify the bacterial infection and viral infection, which can provide a reliable basis for clinical treatment.