A total of 204 patients were classified into Gram-positive bacterium group (25 cases), Gram-negative bacterium group (89 cases) and negative control group (90 cases). The levels of PCT, CRP, CD64, IL-6 and TNF-α among the groups were determined. The diagnosis performance of PCT and other indices was evaluated by receiver operating characteristic (ROC) curve.

The PCT levels in Gram-negative bacterium group, Gram-positive bacterium group and negative control group were 10.01, 5.80 and 1.06 μg/L, and there was statistical significance among the 3 groups(P<0.01). The differences of CRP, IL-6 and TNF-α among the 3 groups had statistical significance (P<0.05). The levels of CD64 in Gram-positive and Gram-negative bacterium groups were obviously higher than that in negative control group (P<0.01), but there was no statistical significance between Gram-positive and Gram-negative bacterium groups (P>0.05). When the cut-off value of PCT was 0.41 μg/L, the area under the ROC curve of PCT for identifying bacterium infection was 0.882. The sensitivity was 85.1%, and the specificity was 82.2%, which were higher than those of the other 4 indices. For the differential diagnosis of Gram-positive and Gram-negative bacterium groups, the cut-off values of PCT, CRP, IL-6 and TNF-α were 1.25 μg/L, 79.34 mg/L, 27.4 pg/mL and 20.5 pg/mL, and the areas under the ROC curves were 0.671, 0.625, 0.654 and 0.619. The positive predictive values were 88.6%, 83.1%, 88.5% and 90.4%. The area under the ROC curve of PCT was biggest. The sensitivity was 69.7%, and the specificity was 72%. The positive predictive value reached 88.6%.

PCT can be used to the early diagnosis bacterium infection and the differential diagnosis of Gram-positive bacterium and Gram-negative bacterium infections, but the diagnosis performance is weak.