Abstract: Biomarkers to guide antibiotic treatment decisions have been proposed as  an effective way to enhancing a more appropriate use of antibiotics. As  a biomarker, procalcitonin (PCT) has been found to have good  specificity to distinguish bacterial from non-bacterial inflammations.  Decisions regarding antibiotic use in an individual patient are complex  and should be based on the pre-test probability for bacterial infection,  the severity of presentation and the results of PCT serum  concentration. In the context of a high pre-test probability for  bacterial infections and/or a high-risk patient with sepsis, monitoring  of PCT over time helps to track the resolution of infection and  decisions regarding early stop of antibiotic treatment. As outlined by  the Evidence Based Laboratory Medicine (EBLM), not only the pre-test  probability but also the positive likelihood ratio influence the  performance of a test do be really diagnostic. This aspect should be  taken into account in the interpretation of the results of clinical  trials evaluating the performance of PCT in guiding antibiotic therapy.

Keywords: Evidence Based Laboratory Medicine (EBLM); Procalcitonin (PCT); antibiotic therapy.