CALCA and bacterial infectious disease: Diagnosis of bacterial infection is challenging because of the ambiguous clinical sign and limitation of microbial techniques.27 The causative microorganism cannot be detected in up to 80% of patients with suspected blood stream infections.14,28 Because of these facts there is a lack of a gold standard for invasive bacterial infection.19 Because of these diagnostic uncertainty several studies have analyzed the role of surrogate biomarkers like PCT to estimate the likelihood for presence of a bacterial infection in various clinical situations.27