LabMed

Pneumonia, Infectious

At a Glance

Pneumonia can present with a variety of signs and symptoms, including cough, fever, chest pain, dyspnea, empyema, and cough productive of profuse or bloody sputum. Physical examination may detect signs of consolidation, such as crackles, rales and rhonchi, diminished breath sounds, dullness to percussion, radiographic infiltrates, cavitary lesions, and empyema.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Gram stain and bacterial culture of a deeply coughed sputum collected first thing in the morning, tracheal aspiration, bronchoscopy specimen, or transtracheal aspirate should be ordered.

Special culture techniques, special stains, serologic assays, urinary antigen assays, or lung biopsies are required to identify some pathogens, such as mycobacteria, mycoplasmas, anaerobic bacteria, chlamydiae, viruses, fungi, legionellae, rickettsiae, and parasites.

Rapid direct (nonculture) detection of virus-infected cells using immunofluorescence (DFA or direct fluorescent antibody) has a turnaround of less than 1 day and may be diagnostically helpful, since viral culture results can take several days to weeks; however, the test may still be negative in the presence of viral infection.

Viral culture specimens should be collected as soon as possible after onset of the disease to preserve sensitivity.

Polymerase chain reaction (PCR) testing is not available at all institutions; however, if a rapid diagnosis would provide immediate changes in clinical therapy, as in severely ill or immunocompromised patients, the increased cost of testing may be warranted.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Expectorated sputum cultures for identifying bacterial pathogens can be misleading because of normal oropharyngeal flora contamination during passage through the upper airways. Most reliable specimens are from normally sterile sites.

Up to one-half of patients may have no identifiable pathogen despite a clinical impression of bacterial pneumonia.

Specimens for viral culture should be brought to the laboratory in viral holding media as quickly as possible to ensure sensitivity. Negative viral culture does not rule out a viral etiology.

What Lab Results Are Absolutely Confirmatory?

Culture isolation is absolutely confirmatory.

Etiologic agents include Streptococcus pneumoniae (the most common etiology of bacterial pneumonia), anaerobic bacteria, Staphylococcus aureus, Haemophilus influenzae, Chlamydia pneumoniae, C. psittaci, C. trachomatis, Moraxella (Branhamella) catarrhalis, Legionella pneumophila, Klebsiella pneumonia, and other gram negative bacilli; Mycoplasma pneumoniae (older children and young adults in spring); respiratory syncytial virus (RSV), parainfluenza virus, influenza A and B, adenovirus, Epstein-Barr virus, coxsackievirus, Hantavirus, varicella-zoster virus, and CMV (cytomegalovirus); Nocardia and Actinomyces spp.; mycobacteria, including Mycobacterium tuberculosis, M. kansasii, and M. avium-intracellulare; fungi, including Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis, Cryptococcus neoformans, Aspergillus fumigatus, Mucor spp., Sporothrix schenckii, and Pneumocystis jirovecii; and rickettsiae, primarily Coxiella burnetii (Q fever).

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