What diagnostic tests should be done for suspected fungal pneumonia?

Diagnostic Tests for Suspected Fungal Pneumonia

For suspected fungal pneumonia, a comprehensive diagnostic approach should include high-resolution CT imaging of the lungs, followed by bronchoalveolar lavage (BAL) with multiple specific tests including direct microscopy, culture, galactomannan testing, and appropriate antigen/antibody testing based on clinical context and suspected fungal pathogen. 1

Initial Imaging

• High-resolution or multislice CT scan of the lungs is the diagnostic imaging method of choice and should be performed within 24 hours of clinical suspicion 1
• Conventional chest radiographs are not recommended due to poor sensitivity for detecting early fungal pneumonia 1
• CT imaging without contrast is generally sufficient in most cases 1

Bronchoscopy and Bronchoalveolar Lavage (BAL)

• Bronchoscopy with BAL should be performed at a segmental bronchus supplying an area with radiographic abnormalities 1
• BAL should be performed using a standardized protocol within 24 hours of clinical indication 1
• Samples must be sent immediately to the laboratory for processing within 4 hours 1
• Transbronchial biopsies are not recommended in neutropenic or thrombocytopenic patients due to bleeding risk 1

Microbiological Testing of BAL Samples

• Direct microscopy with calcofluor white stain for rapid visualization of fungal elements 1
• Fungal culture on appropriate media (gold standard but limited by sensitivity of 30-60%) 1
• Cytopathology and histopathology when tissue samples are available 1
• BAL galactomannan (GM) testing for suspected invasive aspergillosis (strong recommendation, high-quality evidence) 1

Serum Biomarkers

• Serum galactomannan (GM) testing for suspected invasive pulmonary aspergillosis, especially in immunocompromised patients (strong recommendation, high-quality evidence) 1
• Serum (1→3)-β-D-glucan (BDG) testing for invasive fungal infections, though should not be relied upon solely for diagnostic decision-making (conditional recommendation, low-quality evidence) 1
• Serum antibody testing specific to suspected fungal pathogens based on clinical presentation and geographic exposure 1

Pathogen-Specific Testing

For Aspergillosis:

• Serum and BAL galactomannan testing (sensitivity 74%, specificity 85% at cutoff of 0.5) 1
• Aspergillus PCR testing of blood or BAL samples 1

For Endemic Mycoses (Blastomycosis, Coccidioidomycosis, Histoplasmosis):

• Serum antibody testing specific to the suspected pathogen 1
• Urine antigen testing when available 1
• For coccidioidomycosis, use multiple diagnostic tests including direct visualization, culture, and serology 1
• For blastomycosis, serum antibody testing against BAD-1 antigen 1

Special Considerations

• In immunocompromised patients with hematological malignancies, multiple diagnostic tests should be performed simultaneously due to high mortality risk 1
• In patients from endemic areas with suspected community-acquired pneumonia, initial serological testing with close follow-up and serial testing is recommended 1
• Specimens for fungal culture and other laboratory studies should be obtained prior to initiating antifungal therapy whenever possible 2
• If therapy must be started empirically, diagnostic testing should still be performed, and treatment adjusted based on results 2

Important Caveats

• False-positive galactomannan results may occur in patients undergoing chemotherapy or with mucositis 1
• Sensitivity of fungal cultures from BAL is limited (30-60%) 1
• Direct microscopy allows early presumptive diagnosis in approximately 73% of fungal and mycobacterial infections 3
• No single test has sufficient sensitivity to rule out fungal pneumonia; multiple complementary tests are needed 1
• Diagnostic yield is highest when combining imaging, microbiological testing, and serological markers 3, 4