Determining the Clinical Utility of an Absolute Procalcitonin Value for Predicting a Positive Culture Result

Abstract

Various procalcitonin ranges have been established to guide antimicrobial therapy; however, there are no data that establish whether the initial procalcitonin value can determine the likelihood of a positive culture result. This study aimed to establish if the initial procalcitonin value, on clinical presentation, has a positive predictive value for any positive culture result. This was a retrospective study of 813 medical intensive care unit patients. Data collected included patient demographics, procalcitonin assay results, sources of infection, culture results, and lengths of stay. Patients were excluded if they were immunocompromised. The primary outcome of this study was to determine a procalcitonin value that would predict any positive culture. Secondary outcomes included the sensitivity, specificity, positive predictive value, and negative predictive value for procalcitonin. After exclusions, a total of 519 patient charts were reviewed to determine the impact of the initial procalcitonin value on culture positivity. In our analyses, the receiver operating characteristic values were 0.62 for all cultures, 0.49 for pulmonary infections, 0.43 for urinary tract infections, and 0.78 for bacteremia. A procalcitonin value of 3.61 ng/ml was determined to be the threshold value for a positive blood culture result (prevalence, 4%). For bacteremia, the sensitivity of procalcitonin was 75%, the specificity was 72%, the positive predictive value was 20%, and the negative predictive value was 97%. Procalcitonin was a poor predictor of culture positivity. An initial procalcitonin value of less than 3.61 ng/ml may be useful in predicting whether bacteremia is absent. Procalcitonin should not be used as the only predictor for determining initiation of antibiotic therapy.KEYWORDS biomarkers, diagnostics, procalcitonin, sepsis S epsis is a leading cause of death and disability in the United States (1, 2). Mortality from sepsis increases with each hour that anti-infective therapy is delayed (3). The impetus for promptly initiating appropriate broad-spectrum antimicrobial therapy must be weighed against the concern for reducing unnecessary antimicrobial therapy and potential harms, such as drug resistance, Clostridium difficile infections, and adverse drug effects (3). The lack of a specific test to assist clinicians in early decision-making regarding initiation and discontinuation of antimicrobial therapy for severe infection and presumed sepsis has led to expanded interest in inflammatory biomarkers, such as procalcitonin (PCT) (4-12).Previous trials evaluating PCT have used value ranges to guide clinical decisions within the construct of initiating and discontinuing antimicrobial therapy using clinical criteria (4,5,(7)(8)(9)(10)(12)(13)(14). By using serial measurements and established cutoff values in intensive care units (ICUs), these studies have shown that PCT values guide antimicrobial therapy (13-18). However, no reports have described the utility of using initial PCT levels to guide upstream anti-infective...

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