[Clinical significance of coagulase-negative Staphylococci isolated from blood culture samples of patients with hematological disorders; true bacteremia or contamination].

In recent years, findings of coagulase-negative Staphylococci (CNS) have been increasing on blood culture tests taken from patients with hematological disorders; however, the diagnosis of true bacteremia is often very difficult because CNS is an indigenous bacterium of the skin. We investigated the relationship between the time from obtaining the blood specimen to the detection of positive culture tests as well as the significance of the pathogen detected. Twenty-three inpatients demonstrated CNS-positive blood culture tests. It was judged that six patients (26%) had contamination, while 17 patients (74%) had true bacteremia. The mean interval until positive culture was 45.3 and 13.9 hours, respectively (p<0.005). The cut-off value for predicting true bacteremia was assumed to be 24 h; sensitivity was 94% and specificity was 83%. The interval until blood culture becomes positive will be a useful marker for accurately diagnosing true bacteremia.