Blastomycosis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: ; Vidit Bhargava, M.B.B.S [2] Aditya Ganti M.B.B.S. [3]


Once suspected, the diagnosis of blastomycosis can usually be confirmed by demonstration of the characteristic broad based budding organisms in sputum or tissues by KOH prep, cytology, or histology.

Laboratory Findings

  • Culture of the organism is the definitive diagnostic test in diagnosing blastomycosis, but due to slow growing nature of the organism it can delay in treatment up to several weeks. [1]
  • Culture on dextrose sabourd agar at 25 to 30°C for 4 to 6 weeks is normally employed. Highest diagnostic yield is of bronchoscopy derived fluid, followed by sputum.
  • Real time PCR is being experimentally tested for direct diagnosis from culture or tissue. [2]
Infection Specimen
Pneumonia Sputum, bronchoalveolar lavage
Cutaneous lesions Deep tissue biopsy, scrapings and exudate
Oseous lesions Joint fluid, synovial tissue biopsy specimen

Prostate biopsy specimen, urine

CNS Cerebrospinal fluid
  • KOH preparation - shows a broad based budding yeast multinucleate yeast cell, round to oval, 8 to 15 μm in diameter with thick, refractile cell walls. Periodic acid-Schiff stain (PAS), PAS with hematoxylin counterstain, and Grocott-Gomori's methenamine silver stain are some of the stains employed.
  • Tissue biopsy of skin or other organs may be required in order to diagnose extra-pulmonary disease. A granulomatous inflammation might be suggestive of fungal presence but is not diagnostic.
  • Commercially available urine antigen testing appears to be quite sensitive in suggesting the diagnosis in cases where the organism is not readily detected. It appears to be more helpful than serum antigen testing.
  • Serological testing is limited in utility by the fact that there is a considerable overlap with other fungal antigens.
  • Sometimes blood and sputum cultures may not detect blastomycosis, lung biopsy is another option, and results will be shown promptly.


  1. Saccente M, Woods GL (2010). "Clinical and laboratory update on blastomycosis". Clin. Microbiol. Rev. 23 (2): 367–81. doi:10.1128/CMR.00056-09. PMC 2863359. PMID 20375357.
  2. Sidamonidze, K.; Peck, MK.; Perez, M.; Baumgardner, D.; Smith, G.; Chaturvedi, V.; Chaturvedi, S. "Real-time PCR assay for identification of Blastomyces dermatitidis in culture and in tissue". J Clin Microbiol. 50 (5): 1783–6. doi:10.1128/JCM.00310-12. PMID 22403418.