Clinical research study
C-Reactive Protein Is an Independent Predictor of Severity in Community-acquired Pneumonia

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Abstract

Background

C-reactive protein (CRP) is an acute phase protein synthesized by the liver primarily in response to interleukin-6. Initial studies have suggested that inflammatory markers may have a role in predicting severity. We investigated whether admission and day 4 CRP could predict severity in community-acquired pneumonia.

Methods

A prospective study was carried out over a 2-year period in a large teaching hospital. CRP was measured on admission and on day 4. The outcomes of interest were: 30-day mortality; need for mechanical ventilation and/or inotropic support; development of complicated pneumonia (lung abscess, empyema, or complicated parapneumonic effusion); the value of predictive tests were assessed using multivariate logistic regression.

Results

There were 570 patients included in the study; 30-day mortality was 9.6%. Low CRP levels showed a high negative predictive value for excluding 30-day mortality (CRP <10 mg/L = 100%, CRP <50 = 99.1%, CRP <100 = 98.9%, CRP <200 = 94.9%). Low admission CRP levels <100 mg/L were independently associated with reduced 30-day mortality (odds ratio [OR] 0.18; 0.04-0.85), P = .03; need for mechanical ventilation and/or inotropic support (OR 0.21; 0.14-0.4), P = .002; and complicated pneumonia (OR 0.05; 0.01-0.35), P = .003. A CRP that fails to fall by 50% or more within 4 days of admission is independently associated with increased 30 day mortality (OR 24.5; 6.4-93.4), P <.0001; need for mechanical ventilation and/or inotropic support (OR 7.1; 2.8-17.8), P <.0001 and complicated pneumonia (OR 15.4; 6.32-37.6), P <.0001.

Conclusions

Admission CRP <100 mg/L has reduced risk for 30-day mortality, need for mechanical ventilation and/or inotropic support, and complicated pneumonia. Failure of CRP to fall by 50% or more at day 4 leads to an increased risk for 30-day mortality, need for mechanical ventilation and/or inotropic support, and complicated pneumonia. C-reactive protein is an independent marker of severity in community-acquired pneumonia.

Section snippets

Methods

We conducted a prospective study of all adult patients admitted between February 2005 and February 2007 with a primary diagnosis of community-acquired pneumonia. Ethical approval was obtained from the Lothian research ethics committee.

The main inclusion criteria were presentation to hospital with a diagnosis of community-acquired pneumonia within the study period (February 2005 to February 2007) and the absence of any exclusion criteria. Community-acquired pneumonia was defined as a history

Results

There were 936 patients considered for inclusion during the study period; 570 patients met the criteria and were included in the study. Reasons for exclusion are shown in Table 2.

Baseline characteristics of the study population are shown in Table 3. Characteristics are shown for the whole population and for those patients who had repeat C-reactive protein measurements available during the first 4 days of treatment.

Of all patients, 20.7% were discharged within 24 hours of admission; 13.5%

Discussion

In this study, low CRP levels (<100 mg/L) have high negative predictive values in excluding 30-day mortality, requirement for invasive ventilation and/or inotropic support, and complicated pneumonia. In addition, repeat measurement of CRP at day 4 is shown to be a powerful marker of treatment response—patients in whom the CRP level falls by 50% or more in 4 days have low rates of 30-day mortality, requirement for invasive ventilation and/or inotropic support, and development of complicated

Conclusion

Low admission C-reactive protein levels <100 mg/L effectively excludes severe community-acquired pneumonia and can be used as an adjunct to clinical judgment to identify low-risk patients who may be safely discharged. C-reactive protein <100 mg/L provides a high negative predictive value comparable with CURB65 and PSI severity rules. In patients admitted to the hospital, a CRP level that falls by 50% or more in 4 days indicates a low risk of 30-day mortality, need for mechanical ventilation

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