Blastomyces — Serology

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
Serologic (antibody) testing for Blastomyces dermatitidis complex (Blastomyces dermatitidis and Blastomyces gilchristii),causative agents of blastomycosis, is available at Public Health Ontario. Please note, the specific organism serologic test request must be clearly indicated on the requisition form.

Fungal infections can be challenging to diagnose as symptoms are often non-specific and can mimic bacterial, viral, other fungal infections or malignancy. Culture remains the gold standard for the diagnosis of most invasive fungal infections; however, results of fungal serological tests can often be used to aid in the diagnosis and/or management of specific fungal infections and fungal allergies.

B. dermatitidis complex is endemic to large areas of North America. In Canada, blastomycosis occurs most commonly in Manitoba, Quebec, and Ontario; however, cases have also been reported in other provinces. Northwestern Ontario is a hyperendemic region, although cases have been identified across the province. In the United States, endemic areas include Michigan, Wisconsin, Minnesota, and the Mississippi and Ohio River valleys. Blastomycosis is typically acquired through the inhalation of airborne fungal spores released when contaminated soil, decaying vegetation, or other organic material is disturbed. Exposure to soil, decaying wood, vegetation, waterways, and activities involving soil disturbance may increase the likelihood of infection.

Blastomycosis infection can occur in otherwise healthy or immunocompromised individuals typically initially presenting as respiratory illness. The infection may disseminate to other organs, particularly in immunocompromised individuals.

For information on fungal culture please refer to:

For other fungal serology testing refer to:

Updates as of September 14, 2026

This page contains test information specific to Blastomyces Serology and replaces the information previously published under Fungal Serology.

*Uncontrolled print copy. Valid only on day of print: 14 Sep 2026.

Testing Indications

Blastomycosis is a fungal infection that can present in outpatient settings as a community-acquired pneumonia with non-specific symptoms such as fever, cough, fatigue, night sweats, myalgias, and arthralgias. In more severe cases, patients may present to the emergency department with severe pneumonia, respiratory failure, or acute respiratory distress syndrome requiring hospitalization. Extrapulmonary disease involving the skin, bones, central nervous system, and other organs may also occur.

While highly specific, serologic testing via immunodiffusion is not recommended as a diagnostic assay for blastomycosis due to low sensitivity¹; for diagnosis of blastomycosis, submission of specimens for microscopy and culture are recommended. Refer to Blastomyces — Culture and Identification. Serology may aid in determining if a patient has been exposed to Blastomyces but should not be used as a stand-alone test for diagnosis.¹

Acceptance/Rejection Criteria

Test request is rejected if:

inappropriate specimen type is submitted
specimen volume is insufficient for testing
required patient information and relevant clinical history are not provided on the requisition
specific fungal agent’s name (i.e. Blastomyces) is not specified on the requisition. “Fungal serology” is not an acceptable request.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Blastomyces Serology¹	General Test Requisition	Serum	1.0 ml serum	Collect blood in serum separator tubes (SST)

Submission and Collection Notes

Complete all fields of the requisition form, including:

Test(s) requests (indicate the specific fungus/fungi being requested) and indication(s) for testing.
Patient setting/population/source
Travel history to endemic area
Symptoms
Onset date

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

The specific fungal test(s) must be clearly indicated on the requisition. Requests submitted only as ‘fungal serology’ will be cancelled.

Timing of Specimen Collection

An acute serum sample (collected early after the symptom onset) and a convalescent (collected 2–3 weeks later) may be required for laboratory diagnosis.

Limitations

Haemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing.

Storage and Transport

Centrifuge serum if using SST.

Samples should be stored at 2–8°C following collection and shipped on ice packs to PHO as soon as possible. For transportation, place specimen in biohazard bag and seal.
All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Blastomyces testing is performed once per week at Public Health Ontario’s Toronto location.

TAT is up to 10 business days after receipt.

Test Methods

Blastomyces serology is tested by immunodiffusion and detects A band precipitins.

Limitations:
A negative result does not rule out the possibility of current infection or previous exposure.

Interpretation

The following table provides possible test results with associated interpretations:

Blastomyces dermatitidis Immunodiffusion
Result	Interpretation	Comments
Non-Reactive A Band	No detectable level of antibody against Blastomyces dermatitidis	A negative test does not exclude a diagnosis of blastomycosis. If blastomycosis is suspected submit a new specimen for repeat serology or submit appropriate specimens for culture.
Partial A Band	Blastomyces dermatitidis antibody status inconclusive. Resubmit if clinically indicated.
Reactive A Band	Serologic evidence of infection.

Blastomyces dermatitidis serology results are reported as “Non-Reactive”, “Partial” or “Reactive”. Reactive results will indicate presence of A band (precipitins). The A band may be reported as partial band which is an indeterminate result. Reactive A band provides presumptive evidence of infection.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

References

Theel ES, Kus JV, Grys TE, Ampel NM, Schwartz IS, Zhang SX. Practical guidance for clinical microbiology laboratories: antibody and antigen detection methods for dimorphic fungal infections. Clin Microbiol Rev. 2025;38(2): e00005-20. Available from: https://journals.asm.org/doi/10.1128/cmr.00005-20#