NEW YORK (Reuters Health) – An analysis of the sensitivity of several diagnostic tests for histoplasmosis indicates that combining antigen and antibody testing, as well as culture and pathology, is the most reliable way to detect the infection – but it’s not infallible.

“Importantly,” say the authors of the report in Clinical Infectious Diseases online August 2, “the sensitivity of antigen testing is not 100%, even if both urine and serum samples are tested, and negative results do not exclude histoplasmosis.”

Dr. Chadi A. Hage, with the Roudebush VA Medical Center and Indiana University, Indianapolis, and colleagues explain that the diagnosis of histoplasmosis is commonly based on a combination approach, but the sensitivity of different tests have not been examined since improvements were made to the MVista Histoplasma antigen EIA (MiraVista Diagnostics).

To look into this, the team collected serum and urine specimens from 218 patients with histoplasmosis and 229 controls. Among the histoplasmosis group, 158 had disseminated disease and 60 had pulmonary infection.

Among the group with disseminated histoplasmosis, antigenuria was detected in 91.8% of patients, the investigators report. Sensitivity for antigenemia was similar. Culture findings were positive in 74.2% of cases, and similar rates were seen with pathology (76.3%) and antibody testing (75.0%).

Test sensitivities in pulmonary cases varied with acuity. For example, antigenuria was positive in 83.3% of acute cases, in only 30.4% of subacute cases, but 87.5% in chronic cases. On the other hand, antibody results were positive in 66.7%, 95.1% and 83.3% of those three categories, respectively.

The control group included 30 subjects with blastomycosis, and the histoplasmosis tests were 90% cross-reactive in this group. However, the histoplasmosis EIA was 99% specific when tested in healthy subjects and those with nonfungal infections, Dr. Hage and colleagues report

They conclude, “This study supports a broad approach, using antigen testing of urine and serum samples, antibody testing, culture, and pathology for diagnosis of disseminated or pulmonary histoplasmosis.”

Also, they recommend, “Repeated testing is advised for patients with progressive illness if the initial test results are negative.”

Reference:
A Multicenter Evaluation of Tests for Diagnosis of Histoplasmosis
Clin Infect Dis 2011.