Procalcitonin levels in gram-positive, gram-negative, and fungal bloodstream infections

Abstract

Procalcitonin (PCT) can discriminate bacterial from viral systemic infections and true bacteremia from contaminated blood cultures. The aim of this study was to evaluate PCT diagnostic accuracy in discriminating Gram-positive, Gram-negative, and fungal bloodstream infections. A total of 1,949 samples from patients with suspected bloodstream infections were included in the study. Median PCT value in Gram-negative (13.8 ng/mL, interquartile range (IQR) 3.4-44.1) bacteremias was significantly higher than in Gram-positive (2.1 ng/mL, IQR 0.6-7.6) or fungal (0.5 ng/mL, IQR 0.4-1) infections (P < 0.0001). Receiver operating characteristic analysis showed an area under the curve (AUC) for PCT of 0.765 (95% CI 0.725-0.805, P < 0.0001) in discriminating Gram-negatives from Gram-positives at the best cut-off value of 10.8 ng/mL and an AUC of 0.944 (95% CI 0.919-0.969, P < 0.0001) in discriminating Gram-negatives from fungi at the best cut-off of 1.6 ng/mL. Additional results showed a significant difference in median PCT values between Enterobacteriaceae and nonfermentative Gram-negative bacteria (17.1 ng/mL, IQR 5.9-48.5 versus 3.5 ng/mL, IQR 0.8-21.5; P < 0.0001). This study suggests that PCT may be of value to distinguish Gram-negative from Gram-positive and fungal bloodstream infections. Nevertheless, its utility to predict different microorganisms needs to be assessed in further studies.

Figure 1

Comparison of PCT median values according to BC result.

Figure 2

Receiver operating characteristic (ROC) curves of different cut-offs of PCT in differentiating: (a) Gram-negative bacteria from Gram-positive bacteria (AUC 0.765, 95% CI 0.725–0.805; P < 0.0001); (b) Gram-negative bacteria from fungi (AUC 0.944, 95% CI 0.919–0.969, P < 0.0001); (c) Gram-positive bacteria from fungi (AUC 0.763, 95% CI 0.693–0.832; P < 0.0001). Sensitivity, Specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV), Positive Likelihood Ratio (+LR), and Negative Likelihood Ratio (−LR) are reported for the best cut-off values found in each ROC.

Figure 3

Comparison of PCT median values in bloodstream infections by Enterobacteriaceae, non-fermentative Gram-negative bacteria, or obligate anaerobic Gram-negative bacteria.

Figure 4

Receiver operating characteristic (ROC) curve of different cut-offs of PCT in differentiating Enterobacteriaceae from nonfermentative Gram-negative bacteria (AUC 0.691, 95% CI 0.593–0.789, P < 0.0001). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (+LR), and negative likelihood ratio (−LR) of different cut-off values are reported.