Bacteremia is one of the most common causes of mortality in hospitalized patients. Blood culture is currently the recommended method for diagnosing bacteremia. However, a positive result via blood culture does not always mean that bacteremia is present. For example, common skin flora, particularly coagulase-negative staphylococci (CNS), may contaminate blood cultures. It is important to determine whether a positive blood culture reflects a severe threat of sepsis, or occurs due to contaminant of the specimen by normal skin flora. 1 Incorrect interpretation of CNS-positive blood cultures results in unnecessary administration of antibiotics, increases healthcare costs, prolongs hospitalization, and promotes antibiotic resistance in microorganisms. 2 Certain factors help health care professionals determine whether CNS detected via blood culture represents true bacteremia or merely reveals contamination in the specimen. 1 For example, the time to positivity (TTP), which is mainly influenced by the species of bacteria and the original bacterial load, has been used in the interpretation of blood cultures that test positive for CNS. 3 Further, an elevated level of serum procalcitonin (PCT) has been associated with true CNS bacteremia. 4,5,6 Patients with CNS bacteremia have an elevated PCT level and a shortened TTP. We hypothesized that the ratio of TTP to PCT might be a more accurate predictor of CNS bacteremia, compared to PCT, or TTP alone. We retrospectively reviewed blood cultures from 102 individuals with positive results due to CNS to assess the clinical utility of the TTP to PCT ratio in predicting true bacteremia.