Fungal Antigen, Beta-d-Glucan

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Subject: Fungal Antigen, Beta-d-Glucan

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Definition

  • (1-3)-β-d-glucan (BG) is a cell wall component of most fungi, except Zygomycetes and Cryptococcus species. BG has been used as a biomarker for invasive fungal infections (IFI), including candidemia and Pneumocystis pneumonia; an FDA-approved test for quantitative BG detection is available. In patients with ILI or Pneumocystis pneumonia, significant levels of BG may be detected in the serum significantly earlier than clinical signs and symptoms or detection of infection by laboratory or imaging studies. Decreasing BG levels have been associated with treatment success.

Special Collection and Transport Instructions

  • Blood samples are collected and transported according to standard protocol. Samples are allowed to clot and serum separated for testing (minimum 0.5 mL).

Use

  • BG testing may be submitted for early evaluation of patients at risk for IFI or Pneumocystis pneumonia, or to monitor the effectiveness of therapy.

Interpretation

  • Expected result: Not detected.

  • Positive result:

    • For IFI in neutropenic patients, BG levels ≥80 pg/mL are consistent with emerging or active infection (sensitivity approximately 65%; specificity approximately 95%).

    • For Pneumocystis pneumonia, a higher cutoff value (≥100 pg/mL) has been recommended, yielding sensitivity approximately 95% with approximately 99% specificity.

  • Indeterminate result: Detectable BD levels below cutoff values do not establish or reject a diagnosis. Repeat testing is recommended.

  • Negative result: Fungal infection or Pneumocystis pneumonia is unlikely, but infection with Cryptococcus species or Zygomycetes is not ruled out.

Limitations

  • The BG assay is not specific for any specific fungal pathogen. Additional testing is required for identification of the infecting species. Evaluation of patients at risk for IFI or Pneumocystis pneumonia should not be evaluated by BD as the sole diagnostic testing. Fungal culture, wet mount, imaging studies, histopathology and other relevant diagnostic evaluations should be performed as relevant.

 
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