Serum C-reactive protein as a biomarker for early detection of bacterial infection in the older patient.

Background: although C-reactive protein (CRP) is widely used in younger populations, its value for diagnosing bacterial infection in older population is not well established. This study examined the usefulness of serum CRP level in the early detection of bacterial infection in older patients.

Methods: in a prospective cohort study, consecutive patients aged 70 years or over admitted to Aged Care wards were recruited. CRP levels were measured within 24 h of presentation, and their significance in predicting bacterial infections was analysed. The relationship between CRP and other clinical features of diagnosing bacterial infections (e.g. temperature, white cell count, neutrophil count, oxygen saturation, blood pressure and heart rate) was also examined.

Results: a total of 232 patients were recruited over a period of 3 months. CRP levels were 21.3 +/- 36.0 and 150.5 +/- 114.1 mg/l (mean +/- SD) in the non-infection and infection groups, respectively (P < 0.001). We found that the CRP cut-off value of 60 mg/l had the best combination of sensitivity and specificity. At this level, the sensitivity of diagnosing bacterial infection was 80.7%, specificity 96.0%, positive predictive value 91.9% and negative predictive value 89.8%. CRP and temperature had higher sensitivity and specificity than white cell count and neutrophil count in the diagnosis of infection. For every 1-mg/l increment in CRP, the risk of bacterial infection increases by 2.9%.

Conclusion: CRP is a convenient and useful biomarker to predict early bacterial infection in older patients especially when other markers are atypical or not present.