Test Id : HIBAG

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.

1.2 mL

Diagnosing Histoplasma capsulatum or Blastomyces dermatitidis infection without differentiation between the organisms

Monitor antigen levels following initiation of antifungal treatment

Blastomyces dermatitidis and Histoplasma capsulatum are dimorphic fungal agents with increasingly overlapping endemicity throughout the Midwestern, South Central, and Southeastern United States, particularly in regions around the Ohio and Mississippi River valleys, the Great Lakes, and the Saint Lawrence River. These agents are also found in regions of Canada.

These 2 fungi maintain a yeast form in the host at body temperature but are maintained as molds in the environment, which release spores that are inhaled by individuals leading to infection. Through phylogenetic analysis, B dermatitidis has been separated into 2 distinct species: B dermatitidis and Blastomyces gilchristii, both able to cause blastomycosis. B dermatitidis infections are frequently associated with dissemination, particularly in older patients, smokers, and immunocompromised hosts, while B gilchristii has primarily been associated with pulmonary and constitutional symptoms. Additional species of Blastomyces have recently been discovered and characterized; however, the performance characteristics of this assay for these species are unknown.

Approximately half of patients infected with Blastomyces will develop symptoms that are frequently nonspecific, including fever, cough, night sweats, myalgia or arthralgia, weight loss, dyspnea, chest pain, and fatigue. Symptoms may appear anywhere from 3 weeks to 3 months following infection.

For Histoplasma infections, clinical manifestations are largely dependent on the fungal burden at the time of exposure and the patient's underlying immune status. While the vast majority (>90%) of exposed individuals will remain asymptomatic, individuals seeking medical attention can present with a diverse set of symptoms ranging from a self-limited pulmonary illness to severe, disseminated disease. Individuals at risk for severe infection include those with impaired cellular immunity or have undergone organ transplantation, are HIV positive, or have a hematologic malignancy.

Diagnosis of blastomycosis and histoplasmosis relies on a combination of assays, including culture and molecular testing performed on appropriate specimens, and serologic evaluation for both antibodies to, and antigen released from, the organism. Although culture remains the gold standard method and is highly specific, these organisms can take several days to weeks to grow, and sensitivity is diminished in cases of acute or localized disease. Similarly, molecular testing offers high specificity and a rapid turnaround time, however sensitivity is imperfect. Detection of an antibody response to Blastomyces or Histoplasma offers high specificity; however, results may be falsely negative in patients who are acutely ill or are immunosuppressed.

Histoplasma/Blastomyces Antigen Result:

Not Detected

Histoplasma/Blastomyces Antigen Value:

Not Detected

Detected: <1.5 ng/mL

Detected: 1.5-25.0 ng/mL

Detected: >25.0 ng/mL

Reference values apply to all ages.

Not detected: No antigen from Histoplasma or Blastomyces detected. False-negative results may occur depending on extent of disease or site of infection. Repeat testing on a new specimen if clinically indicated.

Detected: Antigen from Histoplasma or Blastomyces (unable to differentiate) was detected, below the limit of quantification (<1.5 ng/mL). Result should be correlated with clinical presentation, exposure history, and other diagnostic procedures, such as culture, serology, histopathology, and radiographic findings to aid in the differentiation between histoplasmosis or blastomycosis.

Detected: Antigen from Histoplasma or Blastomyces (unable to differentiate) detected. Result should be correlated with clinical presentation, exposure history, and other diagnostic procedures, such as culture, serology, histopathology, and radiographic findings, to aid in the differentiation between histoplasmosis and blastomycosis.

Detected: Antigen from Histoplasma or Blastomyces (unable to differentiate) detected, above the limit of quantification (>25.0 ng/mL). Result should be correlated with clinical presentation, exposure history, and other diagnostic procedures, such as culture, serology, histopathology, and radiographic findings, to aid in the differentiation between histoplasmosis or blastomycosis.

Due to significant cross-reactivity between galactomannan antigens from Blastomyces and Histoplasma, this assay does not differentiate between these 2 dimorphic fungal agents. To differentiate, consider fungal culture, molecular testing, or serology testing.

Positive results should be correlated with other clinical and laboratory findings (eg, culture, serology).

Low-level positive antigen levels may persist following resolution of infection and completion of appropriate treatment regimen.

Sensitivity of this assay to detect antigen from species other than Blastomyces dermatitidis or Histoplasma capsulatum is unknown.

False positive results may occur less frequently with other dimorphic agents (eg, Coccidioides).

1. McBride JA, Gauthier GM, Klein BS: Clinical manifestations and treatment of Blastomycosis. Clin Chest Med. 2017 Sep;38(3):435-449

2. Chapman SW, Dismukes WE, Proia LA, et al: Clinical practice guidelines for the management of blastomycosis. Clin Infect Dis. 2008 Jun 15;46(12):1801-1812

3. Wheat LJ, Freifeld AG, Kleiman MB, et al: Clinical practice guidelines for the management of patients with histoplasmosis: 2007 update by the Infectious Diseases Society of America. Clin Infect Dis. 2007 Oct 1;45(7):807-825

The assay detects Blastomyces dermatitidis antigen in human serum samples using specific, proprietary antibodies in an enzyme-linked immunosorbent assay format. The detection method involves an enzyme/substrate system with the level of urinary B dermatitidis antigen proportional to the assay signal. The patient specimen result is compared to a cutoff calibrator and a standard curve of a series of assay calibrators (1.25 to 20.00 ng/mL) to determine the presence or absence of antigen, and if present, to establish a quantitative level of B dermatitidis serum antigen.(Package insert: Blastomyces dermatitidis Serum Antigen Detection Kit. Gotham Biotechnology; V2, R2, 01/2023)

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This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

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