Can serum procalcitonin and C-reactive protein as nosocomial infection markers in hospitalized patients without localizing signs?*

BACKGROUND Early diagnosis of infection with the use of valuable markers leads to decreased mortality and morbidity. The aim of this study was to evaluate the value of procalcitonin (PCT) and C-reactive protein (CRP) for detecting nosocomial infection in hospitalized patients without localizing signs. METHODS We conducted a prospective observational study on 150 hospitalized patients with fever > 38°C emerging 48-72 hours after their admission at Alzahra Hospital, Isfahan, Iran. The subjects did not have any localizing sign of infection. PCT and CRP values were determined using rapid tests and were compared with results of blood culture as the standard test. The sensitivity, specificity, positive and negative predictive values (PV) and likelihood ratios (LRs) were calculated for both PCT and CRP. Receiver operating characteristic (ROC) curves were also used to evaluate the diagnostic value of the PCT and CRP for detecting nosocomial infections. Finally, the areas under the resulting curves were compared. RESULTS PCT had a sensitivity of 57.1%, a specificity of 89.1%, a positive PV of 46.2%, and a negative PV of 92.7% while the corresponding percentages for CRP test were 76.2%, 48%, 19.3%, and 92.5%. PCT marker also had a higher positive LR and lower negative LR than did CRP marker. The observed areas under the ROC curves were 0.73 for CRP (95% CI, 0.63-0.82; p = 0.023) and 0.80 for PCT (95% CI, 0.68-0.91; p = 0.001). The optimal cut-off values (best diagnostic accuracy) were 39 mg/L for CRP and 7.5 ng/mL for PCT. CONCLUSIONS Determination of PCT and CRP is a valuable tool for identifying nosocomial infections. PCT showed better specificity, negative and positive PV. However CRP showed significantly better sensitivity compared with PCT. Therefore, these tests should be considered as part of initial work-up for patients with unknown source of infection.