C-reactive protein. A clinical marker in community-acquired pneumonia.

Study Objective: To assess the range of plasma C-reactive protein (CRP) in patients presenting with community-acquired pneumonia and to compare the serial changes of this acute-phase protein with clinical outcome.

Design: Prospective hospital-based study, including separate retrospective case series.

Patients: Twenty-eight consecutive patients (mean age, 60 years) admitted to our hospital with community-acquired pneumonia were studied. Serial daily plasma samples were taken and assayed for CRP, tumor necrosis factor-alpha (TNF-alpha), and interleukin 6 (IL-6). Clinical parameters, laboratory data, and response to treatment were recorded. Four other patients considered to be antibiotic failures (three empyemas, one death) were studied separately.

Results: Two patients died. Of those who survived, mean (+/- SD) CRP values for days 1,2,3,4, and 5 were as follows: 136 +/- 43, 96 +/- 44, 53 +/- 36, 54 +/- 43, and 44 +/- 31 mg/L. CRP levels on day 1 in patients who had received antibiotics prior to hospital admission were significantly lower than those who had not, 107 +/- 42 and 152 +/- 44 mg/L (p < 0.05). CRP levels did not correlate with other laboratory parameters or with recognized predictors of mortality. A CRP value that continued to rise despite antibiotic treatment was associated with infective complications or death. Only 52% of patients had detectable TNF-alpha and 24% detectable IL-6 at some point during their hospital stay.

Conclusions: CRP is a sensitive marker of pneumonia. A persistently high or rising CRP level suggests antibiotic treatment failure or the development of an infective complication. These results suggest that CRP, rather than TNF-alpha or IL-6, may have a role as a clinical marker in pneumonia.