Histoplasma antigen detection: A laboratory-based retrospective review of routine testing from 2021 to 2023.

Abstract

Introduction: Progressive disseminated histoplasmosis is associated with high mortality in people with advanced HIV (Human Immunodeficiency Virus) disease or severe immunosuppression. The World Health Organization (WHO) recommends antigen testing for progressive disseminated histoplasmosis diagnosis.

Objective: To assess the positivity of the Histoplasma antigen test in urine specimens referred to SYNLAB.

Materials and methods: A retrospective analysis of SYNLAB's database included specimens referred from February 2021 to August 2023. Specimens were tested using the Clarus Histoplasma GM Enzyme Immunoassay™.

Results: A total of 2442 urine samples were tested, of which 282 (12%) were positive, with a higher positivity rate in adults older than 18 years (12%), compared to patients younger than 18 years (4%). The median Histoplasma antigen concentration was 9.25 EIA (Enzyme Immuno-Assay) units, significantly higher in adult patients (9.6 EIA units) than in patients younger than 18 years (1.45 EIA units). Testing rates increased over time, peaking in the first quarter of 2023 with 358 tests done, including 25 specimens that tested positive (7%).

Conclusion: Overall, we found that one in four patients tested positive. Higher positivity and antigen concentration were observed in adults. These findings highlight the importance of antigen testing in diagnosing progressive disseminated histoplasmosis, particularly in high-risk populations.