Diagnostic markers and assessment of efficacy of antibacterial therapy

In anti-infective therapy, there is a need for objective diagnostic markers to guide the appropriate selection and duration of antibacterial treatment. In the diagnosis and treatment of bacterial infections, three aspects must be considered: the appropriateness of antibacterial therapy, the initiation and evaluation of an effective initial therapy, and termination of the antimicrobial treatment. Repetitive monitoring of procalcitonin (PCT) has been proposed as such a marker in conjunction with the clinical presentation and microbiological sampling of blood, urine, and/or sputum. Different threshold values for PCT in pulmonary infections vs. severe systemic infections (e.g., sepsis) have been proposed. However, a single PCT determination is not sufficient, only consecutive measurements can give feedback of the appropriateness and success of the antibacterial therapy. Furthermore, it is important to realize that besides bacterial infection, other disease states can elevate PCT levels. Examples are calcitonin-producing tumors, medullary C-cell thyroid carcinoma, and acute respiratory distress syndrome (ARDS). PCT can also be elevated in fungal infections. On the other hand, localized and encapsulated infections (e.g., abscess, endocarditis and early stages of infections) can be associated with lowered PCT values.