Clinical Utility of the Time-to-Positivity/ Procalcitonin Ratio to Predict Bloodstream Infection Due to Coagulase-Negative Staphylococci

Abstract

Objective: To develop a novel clinical diagnostic method to distinguish bacteremia from blood contamination due to coagulase-negative staphylococci (CNS) by using the ratio of the time to positivity (TTP) of a blood culture with positive results to its serum procalcitonin (PCT) level. Methods: We retrospectively reviewed the clinical and microbiological records of 102 patients who had 1 or more blood cultures that tested positive for CNS from August 2007 through February 2012. Results: Receiver operating characteristic (ROC) curve analysis indicated that, at a cutoff of 1.24 ng per mL, 21.5 hours, and 22.5 (hours × mL)/ng,the TTP to PCT ratio, PCT level, and TTP yielded the most favorable discrimination for bacteremia caused by CNS, with sensitivities of 85.7%, 78.6%, and 61.9%,respectively, and specificities of 80.0%, 78.3%, and 61.7%,respectively. The TTP to PCT ratio was the most accurate of the studied variables in predicting CNS-triggered bacteremia levels. Conclusion: The TTP to PCT ratio is a useful predictor to differentiate the culture samples that test positive, revealing the presence of CNS bacteremia, from those that are merely contaminated.