Aiding in the diagnosis of Histoplasma capsulatum infection
Monitoring Histoplasma antigen levels in urine
Alongside other routine methods including culture, molecular testing, and serology, this test aids in the diagnosis of infection with Histoplasma capsulatum.
Enzyme Immunoassay (EIA)
HSTQU
Histo
Histoplasma capsulatum
Histoplasma galactomannan antigen
Histoplasma polysaccharide
Urine
Supplies: Sarstedt 5 mL Aliquot Tube (T914)
Container/Tube: Plastic vial
Specimen Volume: 4 mL
Collection Instructions:
1. Collect a random urine specimen.
2. No preservative.
3. Do not centrifuge to remove particulates.
If not ordering electronically, complete, print, and send Infectious Disease Serology Test Request (T916) with the specimen.
2.5 mL
| Gross hemolysis | Reject |
| Turbid Colored | Reject |
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 14 days | |
| Frozen | 31 days | ||
| Ambient | 72 hours |
Aiding in the diagnosis of Histoplasma capsulatum infection
Monitoring Histoplasma antigen levels in urine
Histoplasma capsulatum is a dimorphic fungus endemic to the Midwestern United States, particularly along the Mississippi River and Ohio River valleys. Infection occurs following inhalation of fungal microconidia, and subsequent 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, who have undergone organ transplantation, who are HIV positive, or who have a hematologic malignancy.
The available laboratory methods for the diagnosis of H capsulatum infection include fungal culture, molecular techniques, serologic testing, and antigen detection. While culture remains the gold standard diagnostic test and is highly specific, prolonged incubation is often required, and sensitivity decreases (9%-34%) in cases of acute or localized disease. Similarly, molecular methods offer high specificity but decreased sensitivity. Serologic testing likewise offers high specificity; however, results may be falsely negative in immunosuppressed patients or those who present with acute disease. Also, antibodies may persist for years following disease resolution, thereby limiting the clinical specificity.
Detection of H capsulatum antigen from urine samples has improved sensitivity (80%-95%) for the diagnosis of active histoplasmosis compared to both culture and serology. Additionally, urine antigen levels can be followed to monitor patient response to therapy, with declining levels consistent with disease resolution. Notably, however, H capsulatum antigen may persist at low levels following completion of antifungal therapy and clinical improvement.
HISTOPLASMA ANTIGEN RESULT:
Not Detected
HISTOPLASMA ANTIGEN VALUE
Not Detected
Detected: <0.2 ng/mL
Detected: 0.2-25.0 ng/mL
Detected: >25.0 ng/mL
Not Detected: No Histoplasma antigen detected. False-negative results may occur. Repeat testing on a new specimen should be considered if clinically indicated.
Detected, <0.2 ng/mL: Histoplasma antigen detected below the limit of quantification (<0.2 ng/mL). Results should be correlated with clinical presentation, exposure history and other diagnostic procedures, including culture, serology, histopathology, and radiographic findings. False-positive results may occur in patients with other fungal infections, including Blastomyces.
Detected: Histoplasma antigen detected. The reportable range of this assay is 0.2 to 25.0 ng/mL. Results should be correlated with clinical presentation, exposure history, and other diagnostic procedures, including culture, serology, histopathology, and radiographic findings. False-positive results may occur in patients with other fungal infections, including Blastomyces.
Detected, >25 ng/mL: Histoplasma antigen detected above the limit of quantification (>25.0 ng/mL). Results should be correlated with clinical presentation, exposure history, and other diagnostic procedures, including culture, serology, histopathology, and radiographic findings. False-positive results may occur in patients with other fungal infections, including Blastomyces.
Low-level positive titers may persist following resolution of infection and completion of appropriate treatment regimen.
Turbid urine specimens, containing excess protein, cells, or particulate matter, can inhibit the function of the test.
1. Theel ES, Harring JA, Dababneh AS, Rollins LO, Bestrom JE, Jespersen DJ: Reevaluation of commercial reagents for detection of Histoplasma capsulatum antigen in urine. J Clin Micrbiol. 2015 Apr;53(4):1198-1203. doi: 10.1128/JCM.03175-14
2. 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 IMMY Clarus Histoplasma GM Enzyme Immunoassay (EIA) is an immunoenzymatic, sandwich microplate assay which detects Histoplasma galactomannan in urine. Galactomannan is a polysaccharide found in the cell wall. Monoclonal anti-Histoplasma IgG antibodies bound to microwell plates are used as capture antibodies. Horseradish peroxidase (HRP) conjugated anti-Histoplasma monoclonal IgG antibodies are used as detection reagents. Urine specimens are run untreated. The samples are added to the microwells coated with the capture antibodies and incubated.
If the patient specimen contains Histoplasma galactomannan, those antigens will become bound to the capture antibodies on the microwells. After incubation, the microwells are washed to remove unbound patient material. HRP detection antibodies are added to the microwells. After a second incubation, the microwells are washed to remove any unbound HRP detection antibodies. If antigen is present in the patient sample, a blue color develops with the addition of 3,3’,5,5’ tetramethylbenzidine (TMB). The reaction is stopped by the addition of a stop solution, where a yellow color develops. The optical density (absorbance) is checked with a microplate reader at 450 nm and a reference wavelength of 620/630 nm.(Package insert: Clarus Histoplasma GM Enzyme Immunoassay. IMMY; Rev. 0 05/08/2019)
Monday through Sunday
This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
87385
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| HSTQU | Histoplasma Ag, Quant EIA, U | 48952-6 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| HISTF | Histoplasma Ag Result | 44524-7 |
| DEXUH | Histoplasma Ag Value | 48952-6 |