Diagnostic value of procalcitonin and C-reactive protein as markers of systemic and localized bacterial infections

Objective To investigate procalcitonin(PCT)and CRP as markers of systemic and localized bacterial infections.Methods The cases of infectious diseases were recruited retrospectively in a children' hospital. Severe sepsis, septicemia with positive blood culture were recruited as systemic bacterial infection group. Acute suppurative tonsillitis, urinary tract infection and pyogenic osteomyelitis and septic arthritis were recruited as localized bacterial infection group. Infectious mononucleosis, hand foot and mouth disease were recruited as viral infection group. The value and positive rates of serum PCT and CRP among these groups were compared. The receiver operator characteristic curve (ROC) was drawn for PCT and CRP to diagnose systemic and localized bacterial infections, and the sensitivity and specificity were evaluated and the area under roc curve (AUC) and 95%CI were analyzed.Results One hundred and forty eight cases were recruited, 19 in systemic bacterial infection group, 55 in localized bacterial infections group and 74 in viral infection group. ①The levels of serum CRP and PCT and the positive rate of PCT were lower in localized bacterial infection group than in systemic bacterial infection group(CRP: 21.35 vs 76.0 mg·L-1, P=0.001; PCT:0.10 vs 28.09 μg·L-1, 32.7% vs 100%, P0.001). The levels of serum CRP and the positive rate were higher in localized bacterial infection group than in viral infection group(21.35 vs 4.0 mg·L-1, P0.001; 73.1% vs 27.0%, P0.001). The levels and the positive rate of serum CRP were not significantly different in these two groups. There were no significant differences of WBC in three groups. The positive rate of WBC was higher in systemic bacterial infection group than in viral infection group(84.5% vs 54.0%,P=0.017),but no significant difference was found between systemic bacterial infection group and localized bacterial infection group. There were no significant differences between localized bacterial infection group and viral infection group.②In patients with localized bacterial infection, the level and the positive rate of serum PCT were higher in systemic inflammatory response syndrome (SIRS) group than non-SIRS group(0.40 vs 0.08, P =0.002; 60.0% vs 17.1%, P =0.001), but there was no significant difference in the level and the positive rate of serum CRP between two groups. ③The AUC of ROC was 0.99 for PCT and 0.84 for CRP to diagnose systemic bacterial infection. It was 0.54 for PCT and 0.78 for CRP to diagnose localized bacterial infection, respectively. Conclusions In our study, PCT was identified as a sensitive marker of systemic bacterial infection and localized bacterial infections progressing into sepsis. As an indicator of bacterial infection, CRP was batter than PCT in localized infections.