Diagnosis of Blastomycosis: A Clinician’s Guide

Blastomycosis diagnosis often begins with an Enzyme Immunoassay (EIA) urine antigen test, recognized for its high sensitivity and rapid results as a noninvasive method. This initial step is crucial for healthcare providers evaluating potential cases. A negative EIA urine antigen test should prompt clinicians to explore alternative diagnoses. However, in situations where clinical suspicion for blastomycosis remains high, further diagnostic investigations are warranted. These may include sputum or bronchoalveolar lavage (BAL) cultures and microscopy, as well as skin biopsies from lesions, also for microscopic examination. Assessing non-pulmonary symptoms affecting the bone, genitourinary system, and central nervous system can also contribute valuable diagnostic information.

While serologic antibody tests are available, their reported low sensitivity means they are typically less reliable as standalone diagnostic tools. They can, however, serve as supplementary tests when antigen tests yield negative results, or to aid in differentiating blastomycosis from histoplasmosis, especially when used in conjunction with Histoplasma antibody testing. In complex cases or when diagnostic uncertainty persists, consulting with specialists in infectious diseases or pulmonology is advisable.

It is important to note that Blastomyces antigen tests exhibit cross-reactivity with Histoplasma. Despite this, it’s clinically relevant because treatment strategies for both infections are largely similar for most manifestations.

For guidance on treatment following a confirmed diagnosis, clinicians should consult the Infectious Diseases Society of America’s blastomycosis treatment guidelines or seek advice from an infectious disease specialist to determine the most appropriate therapy.