To investigate the value of procalcitonin (PCT) kinetics between 0-8-16-24 hours after starting empirical antibiotic therapy in critically ill patients, to predict appropriate or inappropriate antibiotic treatment.

Inclusion Criteria:

• Clinical signs of infection
• Suspected or proven acute infection requiring empiric antibiotic therapy as decided by the attending ICU physician
• Suspected site of infection has to be present and documented
• Microbiological sample sent for staining
• Inflammatory markers available at the start of the therapy

Exclusion Criteria:

• Patients younger than 18 years
• Who received prophylactic or empiric antibiotic therapy 48 hours before inclusion
• Whose receiving acute renal replacement therapy in the first 24 hours following antibiotic treatment
• Following cardiopulmonary resuscitation
• End stage diseases with a "do not resuscitate" order
• Immunocompromised patients (human immunodeficiency virus infection, bone marrow transplantation, malignant haematological disorders and chemotherapy)
• Post cardiac surgery patients

All patients over 18 years with suspected infection on admission or during their stay on the intensive care unit were screened for eligibility. Patients were enrolled, when the attending intensive care specialist had a suspicion of infection and decided to start empirical antibiotic therapy.