Even though a PCT concentration that fulfills adequate sensitivity and specificity and considering that a sensitivity of 73% has been proposed by other authors as satisfactory for PCT [7,21], we could assume that concentrations of 0.49 ng/mL, or better 0.5 ng/ml, with 85% sensitivity and 50% specificity might be useful for the differential diagnosis between a disseminated infection (bacteremia, sepsis and its intermediate stages) and a non disseminated infection (FUO and localized infection). The gene discussed is CALCA; the disease is bacterial infectious disease with sepsis.