Procalcitonin (PCT) is an inflammatory biomarker that rises in bacterial infection and falls in response to antibiotic treatment with greater sensitivity and specificity for bacterial infection than CRP.10,11 It is approved by the US FDA to support antibiotic decision-making in lower respiratory tract infection and in sepsis.12 Nevertheless, current US and UK national guidelines on management of community acquired pneumonia (CAP) recommend against the use of PCT to guide antibiotic prescribing.13,14. The gene discussed is CRP; the disease is bacterial infectious disease.