Clinical study
Performance of a bedside c-reactive protein test in the diagnosis of community-acquired pneumonia in adults with acute cough

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Abstract

Purpose

To evaluate the performance of a rapid, bedside whole blood C-reactive protein test as a diagnostic test for pneumonia in adults.

Methods

We enrolled consecutive adults who presented with acute cough (duration ≤3 weeks). A fingerstick blood specimen for C-reactive protein level was obtained. Patients also provided information about demographic characteristics and symptoms. Physical examination findings, diagnoses, and treatments were abstracted from the medical record; illness duration and subsequent office visits were determined with follow-up telephone calls. A clinical prediction rule for pneumonia was calculated for each patient and compared with C-reactive protein levels.

Results

Twenty (12%) of the 168 patients in the study had radiographic evidence of pneumonia. Median C-reactive protein levels were significantly higher for patients with pneumonia than in the remaining patients (60 mg/L vs. 9 mg/L, P <0.0001). The area under the receiver operating characteristic (ROC) curve for C-reactive protein level as a predictor of pneumonia was 0.83. C-reactive protein level and the clinical prediction rule were independently associated with pneumonia, yielding a combined area under the ROC curve of 0.93. C-reactive protein level was not associated with hospitalization or resolution of symptoms.

Conclusion

C-reactive protein levels could be a valuable addition to clinical prediction rules for pneumonia. A C-reactive protein level ≥100 mg/L might be a useful indication for chest radiography or empiric antibiotic therapy when the diagnosis of pneumonia is in doubt.

Section snippets

Patient sample and setting

Consecutive adults (age ≥18 years) seeking care at the emergency department or acute care ambulatory clinic of the University of California, San Francisco, between January and April 2002, with acute cough (defined as the development of a new cough illness within the past 3 weeks) were eligible for the study. Patients with any of the following self-reported comorbid conditions that alter C-reactive protein levels were excluded: pregnancy, systemic inflammatory disorders (e.g., rheumatoid

Results

Between January and March 2002, 173 adults with acute cough were enrolled in the study, of whom 25 were diagnosed with radiographic pneumonia. Five pneumonia patients were excluded because C-reactive protein levels were not determined; of the remaining 20 patients, 12 were admitted to the hospital. Other causes of cough included bronchitis (n = 30; 20%), unspecified upper respiratory tract infection (n = 102; 69%), and other (e.g., asthma) (n = 16; 11%). One patient without pneumonia was

Discussion

We evaluated the performance of a rapid, bedside C-reactive protein test in the evaluation of adults presenting with acute cough, and found that levels ≥100 mg/L were highly specific for a diagnosis of pneumonia, whereas only a small minority of pneumonia patients (3 of 20) had levels <11 mg/L. When measured at initial presentation, C-reactive protein levels did not discriminate which patients with pneumonia required hospitalization, nor did it correlate with resolution of symptoms 2 to 4 weeks

References (29)

  • J.P. Metlay et al.

    National trends in the use of antibiotics by primary care physicians for adults with cough

    Arch Intern Med

    (1998)
  • R. Gonzales et al.

    Principles of appropriate antibiotic use for treatment of acute respiratory tract infections in adultsbackground, specific aims, and methods

    Ann Intern Med

    (2001)
  • P.S. Heckerling et al.

    Clinical prediction rule for pulmonary infiltrates

    Ann Intern Med

    (1990)
  • J.P. Metlay et al.

    Does this patient have community acquired pneumonia? Diagnosing pneumonia by history and physical examination

    JAMA

    (1997)
  • Cited by (0)

    This study was supported by the Robert Wood Johnson Minority Medical Faculty Development Program. C-reactive protein test kits were provided by the manufacturer (Axis-Shield, Oslo, Norway).

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