Objective: To evaluate PCT as a marker of bacterial community acquired pneumonia in a Danish Hospital setting. To test if it is possible to reduce the use of antibiotics and the length of stay in hospital, and the willingness of the clinicians to take this new marker under advisement in their choice of treatment.

The study is a randomised, controlled intervention study. All adult patients admitted to the Department of Infectious Disease at Skejby hospital suspected of a lower respiratory tract infection (e.g. CAP, acute exacerbation of COPD and bronchitis) are eligible for inclusion. Patients are randomised to have either PCT guided treatment or standard care, in which case the doctor will not learn the PCT test result. In the PCT group the antibiotic treatment will be based on serum PCT as follows: If PCT is less than 0.25 µg/L antibiotic treatment is discouraged; if PCT is greater than 0.25 µg/L antibiotic treatment is encouraged and if PCT is greater than 0.5 µg/L antibiotic treatment is strongly encouraged. The treating doctor is allowed to overrule the treatment guidelines. The control group will receive antibiotics according to usual practice.

The primary endpoints are antibiotic use and length of stay in hospital. Secondary endpoint is the proportion of patients where the treating doctor chooses to disregard the guidelines.

Inclusion Criteria:

• suspected lower respiratory tract infection
• must be able to give consent

Exclusion Criteria:

• age under 18 years
• not able to give consent
• admitted not primarily because of the respiratory tract infection
• hospital acquired infections