CALCA and Recurrent lower respiratory tract infections: A recent study demonstrated that a cut-off between 0.1 and 0.5 ng/mL was applicable in patients with lower respiratory tract infections.[26] Another meta–analysis indicated that a cut-off between 1.0 and 2.0 ng/mL was helpful for identifying patients with sepsis.[27] Therefore, the optimal cut-off values for PCT to detect infection may be related to different organ function status, different types, and sites of infections.