Histoplasma — Serology

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Background
Serologic (antibody) testing for Histoplasma and other fungi is available at Public Health Ontario. Please note, the specific 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.

Histoplasma capsulatum is an endemic, dimorphic fungus that can infect otherwise healthy individuals. Most infected individuals are exposed by inhaling fungal spores from the environment and are present with initial clinical symptoms of respiratory illness. If left untreated, these infections can disseminate, particularly in immunocompromised individuals.

H. capsulatum can be found throughout Canada but is highly endemic in eastern Ontario and Quebec along the St. Lawrence River valley. The Ohio and Mississippi river valleys are also endemic regions. H. capsulatum is also known to be associated with bird and bat droppings.

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 Histoplasma Serology and replaces the information previously published under Fungal Serology.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 14 sept. 2026.

Testing Indications

Serologic testing for Histoplasma capsulatum is indicated in patients with suspected pulmonary or disseminated histoplasmosis, especially in those with subacute or chronic symptoms, and in endemic areas.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. Histoplasma) 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
Histoplasma Serology	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. The specific fungal test(s) must be clearly indicated on the requisition. Requests submitted only as ‘fungal serology’ will be cancelled.
Patient setting/population/source
Travel history to endemic area (if relevant)
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.

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)

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

TAT for Histoplasma serology is up to 10 business days after receipt.

Test Methods

Histoplasma serologyis tested by Immunodiffusion and detects M and H band precipitins.

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

Interpretation

Histoplasma capsulatum serology results are reported as “Non-Reactive”, “Partial” or “Reactive”. Reactive results will indicate presence of M or H bands (precipitins), or both M and H bands. M band is indicative of recent/acute infection, as well as those who have recently recovered from histoplasmosis. H bands appear later and less frequently than M bands, and rarely in the absence of M bands. Bands may be reported as partial which is an indeterminate result.

The following table provides possible test results with associated interpretations:

Histoplasma capsulatum Immunodiffusion
Scenario	M Band Result	H Band Result	Interpretation	Comments
1.	Non-Reactive	Non-reactive	*No detectable level of antibody against Histoplasma capsulatum.*	A Non-Reactive result does not exclude a diagnosis of histoplasmosis. If histoplasmosis is suspected, submit a new specimen for repeat serology or submit appropriate specimens for culture.
2.	Partial	Partial	*Histoplasma capsulatum* antibody status inconclusive. Resubmit if clinically indicated.
3.	Partial	Non-reactive	*Histoplasma capsulatum* antibody status inconclusive. Resubmit if clinically indicated.
4.	Non-reactive	Partial	*Histoplasma capsulatum* antibody status inconclusive. Resubmit if clinically indicated.
5.	Reactive	Non-reactive	Serologic evidence of infection.	Results to be interpreted in the context of the clinical history, signs, and symptoms of the patient.
6.	Reactive	Partial	Serologic evidence of infection.	Results to be interpreted in the context of the clinical history, signs, and symptoms of the patient.
7.	Non-reactive	Reactive	Serologic evidence of infection.	Results to be interpreted in the context of the clinical history, signs, and symptoms of the patient.
8.	Partial	Reactive	Serologic evidence of infection.	Results to be interpreted in the context of the clinical history, signs, and symptoms of the patient.
9.	Reactive	Reactive	Serologic evidence of acute or recent 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#