American Board of Internal Medicine (ABIM) Certification Practice Exam

How is Histoplasmosis usually diagnosed?

1. Blood cultures

2. Detection of histoplasma antigen in body fluids

3. Chest X-ray findings alone

4. Tissue biopsies only

The correct answer is: Detection of histoplasma antigen in body fluids

Histoplasmosis, a fungal infection caused by the organism Histoplasma capsulatum, is typically diagnosed through the detection of histoplasma antigen in body fluids. This method is particularly effective as it allows for the identification of the antigen in urine, serum, or bronchoalveolar lavage fluid, which can provide rapid results and confirm the presence of the infection. Blood cultures are not the most reliable diagnostic tool for histoplasmosis since the organism is often difficult to culture and may not be present in the bloodstream during the acute phase of the disease. Relying solely on chest X-ray findings can suggest the presence of histoplasmosis, but it does not definitively confirm the diagnosis, as many other conditions can mimic these radiographic findings. Similarly, while tissue biopsies can provide histological evidence of the fungus, they are invasive and not always necessary for diagnosis when other non-invasive methods, such as antigen detection, are available and effective. Hence, antigen detection represents a standard and practical approach to diagnosing histoplasmosis.