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

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.