eMedicine Specialties > Emergency Medicine > Pulmonary

Pneumonia, Bacterial: Differential Diagnoses & Workup

Author: James M Stephen, MD, FAAEM, FACEP, Assistant Professor, Tufts University School of Medicine; Attending Physician and Director of Medical Informatics, Department of Emergency Medicine, Associate Director, Kiwanis Pediatric Trauma Service, Tufts Medical Center
Contributor Information and Disclosures

Updated: Oct 15, 2008

Differential Diagnoses

Asthma
Pediatrics, Reactive Airway Disease
Bronchitis
Pediatrics, Respiratory Distress Syndrome
Chronic Obstructive Pulmonary Disease and Emphysema
Pneumonia, Bacterial
Epiglottitis, Adult
Pneumonia, Empyema and Abscess
Foreign Bodies, Trachea
Pneumonia, Immunocompromised
Pediatrics, Bacteremia and Sepsis
Pneumonia, Mycoplasma
Pediatrics, Bronchiolitis
Pneumonia, Viral
Pediatrics, Croup or Laryngotracheobronchitis
Shock, Septic
Pediatrics, Epiglottitis
Pediatrics, Pneumonia

Other Problems to Be Considered

Empyema
Lung abscess

Workup

Laboratory Studies

  • Leukocytosis with a left shift may be observed in any bacterial infection; however, its absence, particularly in patients who are elderly, should not cause the clinician to discount the possibility of a bacterial infection.
  • Leukopenia (usually defined as a WBC count <5000) may be an ominous clinical sign of impending sepsis.
  • Assess ABGs for hypoxia and respiratory acidosis.
  • Blood cultures show poor sensitivity in pneumonia. Even in pneumococcal pneumonia, results are often negative. Their yield may be better in patients with more severe cases. The use of blood cultures only rarely dictates a change in antibiotic use.
  • Hyponatremia (sodium level <130 mEq/L) and microhematuria may be associated with Legionella pneumonia.
    • Sputum examination may be supplemented by using a Legionella -specific fluorescent antibody. However, this technique has a high false-negative rate.
    • Urinary antigen testing for Legionella serogroup 1 organisms is accurate. However, as many as 30% of infections are not caused by serogroup 1 organisms.
    • Pneumococcal antigen tests for serum, urine, and saliva samples have been developed.
    • A Legionella serum antibody titer of 1:128 or more is suggestive of the diagnosis.
    • Antigen-antibody testing has little clinical effect in the ED, although it may help in recalcitrant or unclear cases.
  • Culture pleural effusions or frank empyema fluid, and perform Gram staining.
  • A pulse oximetry finding of <95% indicates significant hypoxia.
  • Consider using the patient's Pneumonia Severity Index (PSI) score as a guide for inpatient care and mortality risk. Note that PSI score may underestimate the patient's need for admission (ie, a young otherwise healthy patient who is vomiting or has social factors that precludes him or her taking the medicine). Conversely, the PSI score tends to overestimate the mortality in the higher risk patients. See PSI calculator.

Imaging Studies

  • Chest radiography
    • Air bronchograms may be observed in the presence of S pneumoniae. Frank consolidation and air bronchograms have been associated with a higher incidence of bacteremia.
    • Cavitary lesions and bulging lung fissures may be observed with Klebsiella pneumoniae infection.
    • Cavitation and associated pleural effusions are observed in cases of S aureus infection, anaerobic infections, gram-negative infections, and tuberculosis.
    • Legionella has a predilection for the lower lung fields.
    • Klebsiella has a tendency to occur in the upper lobes.
  • In unclear cases, high-resolution CT scanning of the lungs may aid in the diagnosis.

Other Tests

  • Sputum examination may be performed.
    • An adequate specimen must have fewer than 10 oral squamous epithelial cells per low-power field.
    • The WBC count should be more than 25 per low-power field.
    • A single predominant microbe should be noted at Gram staining, although mixed flora may be observed with anaerobic infections.
    • Often, patients cannot produce an adequate specimen. Many specimens produced are so contaminated by oral materials that they are unusable.
    • Cultures of the sputum have similar limitations. To be accurate, only specimens that have been examined microscopically and that have satisfied the criteria above should be submitted for culturing.
  • Blood cultures have limited value.
    • Positive findings correlate well with the causative agent.
    • Findings are positive in approximately 40% of cases. (This rate is true even in pneumococcal pneumonia, which has the highest association with positive culture findings.)
    • Cultures require 24 hours (minimum) to incubate.
    • Findings probably have minimal clinical effect in treating bacterial pneumonia.
  • Urine assays are available for the rapid detection of Legionella and pneumococcal antigens. These fast card-type assays have been developed recently, may be performed at the bedside, and may be useful in unclear cases or when the choices for antimicrobial therapy are limited.
  • An elevated international normalized ratio has been associated with more severe illness. This finding may herald the development of disseminated intravascular coagulation.
  • An elevated C-reactive protein level may be predictive of more serious disease. It is has not been clearly shown to differentiate bacterial versus viral illness.

Procedures

  • Bronchoscopy
  • Transtracheal aspiration for culturing
  • Thoracentesis

More on Pneumonia, Bacterial

Overview: Pneumonia, Bacterial
Differential Diagnoses & Workup: Pneumonia, Bacterial
Treatment & Medication: Pneumonia, Bacterial
Follow-up: Pneumonia, Bacterial
Multimedia: Pneumonia, Bacterial
References
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References

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Further Reading

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Contributor Information and Disclosures

Author

James M Stephen, MD, FAAEM, FACEP, Assistant Professor, Tufts University School of Medicine; Attending Physician and Director of Medical Informatics, Department of Emergency Medicine, Associate Director, Kiwanis Pediatric Trauma Service, Tufts Medical Center
James M Stephen, MD, FAAEM, FACEP is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians
Disclosure: Nothing to disclose.

Medical Editor

Dana A Stearns, MD, Assistant Director of Undergraduate Education, Department of Emergency Medicine, Massachusetts General Hospital
Dana A Stearns, MD is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Paul Blackburn, DO, FACOEP, FACEP, Program Director, Department of Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of Surgery, University of Arizona
Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Barry E Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, Program Director, Emergency Medicine, University Hospitals, Case Medical Center
Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

 
 
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