Should a serum (1→3)-β‑D‑glucan test be ordered to evaluate for histoplasmosis?

Should you order serum (1→3)-β-D-glucan (BDG) for suspected histoplasmosis?

No—do not order BDG to evaluate for histoplasmosis; instead, send Histoplasma urine and serum antigen (and add serology or tissue/culture as indicated). 1, 2

Rationale (prioritizing morbidity, mortality, QOL)

• BDG is nonspecific and not recommended to diagnose endemic mycoses; it cannot distinguish Histoplasma from other fungi and yields false positives/negatives that can delay correct therapy and worsen outcomes 1, 3.
• The most informative rapid tests for histoplasmosis that change management and improve outcomes are Histoplasma antigen assays (urine ± serum); combining urine+serum antigen increases sensitivity to ~93%, and adding antibody testing can reach ~96% in acute pulmonary disease 1. Global endemic mycoses guidance also endorses urine/serum Histoplasma antigen for rapid diagnosis and monitoring 2.

What to order instead (actionable sequence)

• High suspicion for histoplasmosis:
  • Order immediately:
    • Urine Histoplasma antigen
    • Serum Histoplasma antigen
  • If pulmonary presentation in immunocompetent host or subacute/chronic disease: add Histoplasma antibody (immunodiffusion/complement fixation) recognizing reduced sensitivity in immunocompromised hosts 1, 2.
  • If disseminated or severe disease suspected: obtain blood/sterile-site cultures and consider tissue biopsy with fungal stains and culture; use results to confirm and guide therapy/monitoring 2.
• If initial antigen negative but clinical suspicion remains high: repeat antigen testing and pursue tissue diagnosis (e.g., bone marrow, lymph node) rather than BDG 2.

Where BDG fits (and pitfalls)

• BDG indicates invasive fungal disease broadly (Candida, Aspergillus, Pneumocystis) and is not specific for Histoplasma; false positives occur with other mycoses and various clinical factors, and false negatives are reported in histoplasmosis 3, 1, 2.
• BDG positivity can occur in histoplasmosis but adds little diagnostic specificity and should not drive treatment decisions for Histoplasma; confirm with Histoplasma-specific antigen/serology/culture/histopathology to avoid mismanagement that could increase mortality 4, 1.
• Do not use BDG to evaluate mucormycosis either (not reliable) 5.

Common caveats to avoid

• Do not substitute BDG for Histoplasma antigen testing.
• Do not rely on a negative BDG to exclude histoplasmosis.
• Beware cross-reactivity and misclassification if using non-specific fungal markers alone; anchor decisions on Histoplasma-specific tests to prevent delays in amphotericin/itraconazole when indicated, which impact survival and QOL in severe/disseminated disease 2.