CALCA and infection: Some studies [46], [47] have similarly found that If PCT levels decrease by more than 30% within the first 24 h of initiating antibacterial treatment, it indicates that the treatment is appropriate and the infection is under control; if PCT levels increase, it means that the antimicrobial treatment must be changed; and if PCT levels continuously increase, the host response to infection is very poor and the patient’s condition is likely to deteriorate.