Diagnostics

Pneumonia is a clinical diagnosis based on history, physical examination, laboratory findings, and CXR findings. Consider microbiological studies and advanced diagnostics based on patient history, comorbidities, severity, and entity of pneumonia

• CBC, inflammatory markers: ↑ CRP, ↑ ESR, leukocytosis

• ↑ Serum procalcitonin (PCT): Procalcitonin is an acute phase reactant that can help to diagnose bacterial lower respiratory tract infections.

  • PCT can be used to guide antibiotic treatment but should not be used to decide if antibiotic therapy is necessary on its own.

  • PCT levels ≥ 0.25 mcg/L correlate with an increased probability of a bacterial infection.

  • Low PCT level after 2–3 days of antibiotic therapy can help facilitate the decision to discontinue antibiotics. [17]

• ABG: ↓ PaO2

• BMP, LFTs

• Lobar pneumonia

  • Opacity of one or more pulmonary lobes

  • Presence of air bronchograms: appearance of translucent bronchi inside opaque areas of alveolar consolidation

• Bronchopneumonia

  • Poorly defined patchy infiltrates scattered throughout the lungs

  • Presence of air bronchograms

• Atypical or interstitial pneumonia

  • Diffuse reticular opacity

  • Absent (or minimal) consolidation

• Parapneumonic effusion

A new pulmonary infiltrate on chest x-ray in a patient with classic symptoms of pneumonia confirms the diagnosis.

Typical pneumonia usually appears as lobar pneumonia on x-ray, while atypical pneumonia tends to appear as interstitial pneumonia. However, the underlying pathogen cannot be conclusively identified based on imaging results alone.

• Indications

  • Inconclusive chest x-ray

  • Recurrent pneumonia

  • Poor response to treatment

• Advantages: more reliable evaluation of circumscribed opacities, pleural empyema, or sites of consolidation

• Findings:

  • Localized areas of consolidation (hyperdense)

  • Air bronchograms

  • Ground-glass opacities

  • Pleural effusion/empyema

    • Hyperdense fluid collection

    • Split pleura sign

  • Nodules

    • Large (e.g., in tuberculosis or fungal pneumonia)

    • Peribronchial (e.g., bronchopneumonia)

    • Disseminated (e.g., septic emboli or varicella-zoster pneumonia)

• Suspected mass (e.g., recurrent pneumonia)

• Need for pathohistological diagnosis (e.g., biopsy of a central mass discovered on CT)

• Inconclusive results on CT

• Poor response to treatment

• Indications: consider if pleural effusion is present to evaluate for pleural empyema