Laboratory Studies
Knowledge of the likely pathogens in afebrile pneumonia syndrome (APS) can guide the selection of laboratory studies. However, detection of one of these organisms is not conclusive evidence of causation because all of them may colonize infants without producing disease.
Complete blood cell count
In patients with APS, the complete blood cell count may reveal a mild eosinophilia, with or without mild leukocytosis.
Serology
Serum immunoglobulin levels are typically moderately elevated.
Tests for Chlamydia trachomatis
Tissue culture isolation of the organism from nasopharyngeal specimens is the most useful test for C trachomatis. If conjunctivitis is present, conjunctival specimens are also helpful. Nonculture techniques include direct fluorescent antibody (DFA) tests and enzyme-linked immunoassays (EIAs).
Polymerase chain reaction (PCR), ligase chain reaction (LCR), and other nucleic acid probe techniques are routinely becoming more widely available. [13, 14]
Serology is useful but takes longer than the above-named tests.
Tests for Cytomegalovirus
Cell culture is the definitive test for CMV. Urine, respiratory secretions, or blood buffy coat (including the shell-vial centrifugation technique) may be used. Polymerase chain reaction and nucleic acid hybridization are becoming more readily available. [15] Serology is often useful, although it takes longer than more direct methods.
Tests for Ureaplasma urealyticum
U urealyticum can be cultured from respiratory secretions. PCR and serology are not routinely available.
Tests for other pathogens
RSV, parainfluenza virus, and adenovirus can be cultured from respiratory secretions, although DFA, EIA, and polymerase chain reaction (PCR) are more rapid and more readily available. P jiroveci is diagnosed using DFA on secretions or biopsy material from the lungs.
Chest Radiography
Chest radiographs may reveal the following [16] :
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Air trapping
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Bronchial wall thickening
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Diffuse interstitial infiltrates (which may be out of proportion to the clinical condition, especially in infants with C trachomatis infection)
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Atelectasis
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Reticulonodular or miliary pattern (rare)
Go to Imaging in Pediatric Pneumonia for more complete information on this topic.
Other Tests
Pulmonary function testing
Results of infant pulmonary function testing (when available) are frequently abnormal in both the acute phase of infection and the long term.
Bronchoalveolar lavage
Bronchoalveolar lavage with or without transbronchial biopsy may be used to collect specimens for diagnosis if the clinical severity warrants.
Histologic findings
Special stains of biopsy material may reveal evidence of particular etiologies. More commonly, direct or indirect fluorescent antibody staining helps identify viral antigens in respiratory secretions (RSV, adenovirus, and parainfluenza).
