Laboratory Tests and Ancillaries
Laboratory tests may not be necessary in uncomplicated pneumonia.
Microbiology
Microbiology aids in determining the causative agent to provide a narrow-spectrum antimicrobial therapy that targets a specific bacterium or virus. Blood culture is not routinely done in nontoxic, fully immunized children with community-acquired pneumonia. This is recommended in patients requiring hospitalization for presumed moderate to severe bacterial CAP, specifically those with complicated pneumonia. This should also be performed in outpatients who do not show clinical improvement and in those with progressive symptoms or clinical deterioration even after starting the antibiotic therapy. A follow-up blood culture is necessary to document resolution of bacteremia caused by S aureus, regardless of the patient's clinical status. A sputum Gram stain and culture are recommended in hospitalized older children and adolescents with more severe disease or in those in whom outpatient therapy has failed.
Tests for Viral Pathogens
Tests that are specific and sensitive to rapidly identify influenza virus, respiratory syncytial virus (RSV), and SARS-CoV-2 (COVID-19) and other respiratory viruses should be done to evaluate children with CAP. A positive influenza test will guide appropriate antiviral agents to be used in both inpatient and outpatient settings and may also decrease the need for additional diagnostic studies and antimicrobial use.
Tests for Atypical Bacteria
School-aged children and adolescents presenting with signs and symptoms of possible Mycoplasma pneumoniae should be tested to identify the appropriate antibiotic to use. However, no single currently available test (ie culture, cold agglutinating antibodies, serology, and molecular-based methods) offers the sensitivity and specificity desired in a clinically relevant time frame.
Ancillary Diagnostic Tests
A complete blood count provides an evaluation of white blood cells (WBC) and determines the presence of anemia or thrombocytopenia, which may guide antimicrobial intervention and identify the presence of hemolytic-uremic syndrome, a rare complication of pneumococcal pneumonia.
Acute-phase reactants (eg peripheral WBC count, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP] concentration, and procalcitonin concentration) should not be routinely done in fully immunized patients with community-acquired pneumonia. This may provide useful information in managing patients requiring hospitalization or those with complications. This may also be helpful in assessing a patient's response to therapy in conjunction with clinical findings.
Pulse oximetry gives an estimate of arterial oxygenation in a non-invasive manner. This is more directly relevant in evaluating severity of disease in community-acquired pneumonia. This should be done in all children with pneumonia and suspected hypoxemia. The presence of hypoxemia will determine the diagnostic tests needed and if hospitalization is warranted. Hypoxemia is a well-established determinant for poor outcomes in children and infants with systemic disease. This is usually monitored continuously in a child with increased work of breathing or significant distress, especially if the patient has a decreased level of activity or agitation.
Imaging
Chest X-ray
A chest X-ray is not necessary to confirm suspected CAP in an outpatient setting since the diagnosis of CAP is strongly suspected based on clinical findings. This cannot differentiate viral from bacterial CAP nor among different possible bacterial pathogens.
A posteroanterior (PA) or lateral chest X-ray is indicated in patients with suspected or documented hypoxemia or significant respiratory distress and in patients who did not respond to initial antibiotic therapy to confirm the presence of possible complications (eg empyema, parapneumonic effusions, necrotizing pneumonia, or pneumothorax). This is also recommended in hospitalized patients to determine the presence, size, and character of parenchymal infiltrates and to document possible complications.
Pneumonia - Community-Acquired Pediatric_Diagnostics
Daily chest X-ray is not required in stable patients with pneumonia complicated by parapneumonic effusion after chest tube placement or after video-assisted thoracoscopic surgery (VATS). A follow-up chest X-ray should not be done routinely in patients who improved uneventfully from community-acquired pneumonia but is recommended in patients who do not show clinical improvement and in those with progressive symptoms or clinical deterioration within 48-72 hours after starting the antibiotic therapy. This should also be obtained in patients with complicated pneumonia who have worsening respiratory distress or clinical instability or in those who are consistently febrile even after 48-72 hours of antibiotic use. This is also recommended after 4-6 weeks in patients with recurrent pneumonia in the same lobe and in patients with lobar collapse at first chest X-ray with suspicion of an anatomic anomaly, chest mass, or foreign body aspiration.
Other Imaging Studies
A chest ultrasound is the imaging study of choice to assess pleural fluid loculations. A chest ultrasound has no ionizing radiation; hence, it is considered a safer imaging procedure than computed tomography (CT). This may be obtained in children with evidence of moderate to large parapneumonic effusion in a chest X-ray. This may be used as a guide in percutaneous needle aspiration for direct culture of infected lung tissue, chest tubing, or thoracentesis.
A CT may also be used to confirm the presence and quantify the amount of pleural fluid. This may be used in assessing atypical infections or the presence of complications.