What type of sample is recommended for beta-2 (beta2) glycan testing in the diagnosis of invasive aspergillosis?

Recommended Samples for Beta-D-Glucan Testing in Invasive Aspergillosis

For beta-D-glucan (BDG) testing in the diagnosis of invasive aspergillosis, serum samples are recommended as the primary specimen type, while bronchoalveolar lavage (BAL) fluid provides complementary diagnostic value. 1

Serum Testing for Beta-D-Glucan

• Serum is the standard sample type for beta-D-glucan testing in suspected invasive aspergillosis, with sensitivity ranging from 50-70% and specificity of 91-99% in patients with hematological malignancies and hematopoietic stem cell transplantation 1
• In ICU and mixed adult populations, serum BDG testing demonstrates sensitivity of 78-85% and specificity of 36-75% for diagnosing invasive aspergillosis, with specificity increasing at higher cut-off values 1
• Serum BDG testing should not be relied upon as the sole diagnostic test for invasive aspergillosis due to its limitations in specificity 1

Bronchoalveolar Lavage (BAL) Fluid Testing

• BAL fluid provides valuable complementary diagnostic information when combined with serum testing 1
• BAL sampling should be performed at a segmental bronchus supplying an area with radiographic abnormalities 2
• BAL samples must be processed within 4 hours of collection to maintain diagnostic accuracy 2
• Combined BAL testing with multiple biomarkers (galactomannan, BDG, and PCR) significantly improves diagnostic yield compared to any single test 3

Diagnostic Algorithm for Invasive Aspergillosis

1. Initial serum testing:

   • Perform serum BDG testing in patients with risk factors for invasive aspergillosis 1
   • Interpret serum BDG results in conjunction with serum galactomannan testing for improved specificity 1

2. Bronchoscopy with BAL when indicated:

   • Perform BAL in patients with negative serum tests but strong clinical suspicion 1, 2
   • Collect BAL samples using standardized protocols for optimal yield 2

3. Comprehensive BAL fluid analysis:

   • Submit BAL fluid for multiple tests including BDG, galactomannan, direct microscopy, culture, and PCR 2, 3
   • The combination of multiple biomarkers in BAL fluid significantly increases diagnostic sensitivity 3

Important Considerations and Pitfalls

• False-positive BDG results may occur in patients with:

  • Early ICU admission (high false-positive rate) 1
  • Concurrent bacterial infections 1
  • Hemodialysis with cellulose membranes 2
  • Receipt of certain blood products 2

• BDG testing alone is unsuitable for ruling out invasive aspergillosis due to its variable sensitivity (57-76%) 1

• Confirmation of positive BDG results with galactomannan testing increases specificity for invasive aspergillosis diagnosis 1

• In critically ill patients, serum BDG testing should not be the sole basis for diagnostic decision-making 1

Special Patient Populations

• In patients with hematological malignancies, serum BDG has a diagnostic sensitivity of 50-70% and specificity of 91-99% 1

• In ICU patients with suspected invasive aspergillosis, serum BDG testing has a high negative predictive value (85-92%), making it useful for excluding disease 1

• For immunocompromised patients with pulmonary infiltrates, combining serum and BAL fluid testing provides the highest diagnostic yield 1, 2