Fungal Biomarkers: Beta-D-Glucan and Aspergillus Galactomannan
Beta-D-Glucan:
 • Polysaccharide cell wall component of many fungi
 • Pathogens: Candida, Aspergillus
    - Other positives: PJP, Histoplasma, Fusarium, Acremonium, Scedosporium, dermatophytes, Coccidioides
    - Negative: Cryptococcus, Mucorales, Blastomyces dermatidis
 • Sensitivity & Specificity:
    - Serum BDG: Sens ~55-96%; Spec ~77-96%
    - Higher specificity for invasive fungal infection (IFI) in hematologic malignancy (HM) pts --> cut-offs defined in clinical context of breakthrough IFI in HM
 • False positives:
    - IVIg, albumin, or other blood products
    - IV penicillin formulations (e.g. amox-clav, not available in US)
    - Hemodialysis with cellulose membranes (most dialyzer membranes synthetic now and should not increase BDG!)
    - Cellulose filters for IV administration
    - Gauze packing of serosal surfaces
    - Infections with other pathogens with cellular beta-glucans (e.g. PsA, Nocardia, mycobacteria)

Aspergillus Galactomannan:
 • Major polysaccharide constituent of Aspergillus cell walls
 • Pathogens: Aspergillus
    - Other Positives: Fusarium, Penicillium, Histoplasma, Blastomyces, Paecilomyces, Cryptococcus
    - Negative: Mucorales
 • Sensitivity & Specificity
    - Serum GM: Sens/Spec ~80% for IA 
    - Most useful in high risk pts with HM and allogeneic HSCT
    - +BAL GM does not differentiate colonization vs invasive disease
    - Sensitivity decreased with: concurrent admin of mold-active antifungals, non-neutropenic pts, SOT recipients, CGD pts
 • False Positives:
    - Pip/Tazo, Amox/Clav (may be + as long as 5d after stopping abxs, but newer formulations post-2010 almost never +GM)
    - IVIg, blood products
    - Use of plasmalyte for BAL solutions causing positive BAL GM
    - +GM more likely in 1st 100d following HSCT; with GIT mucositis or GVHD (leaky gut, translocation)
    - Contamination of food with Aspergillus, closely related fungi 
    - Frozen ice-pops (in setting of GVHD)

ID Chalk Talks by Dr. Sara Dong

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