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

Abstract

Introduction. Progressive disseminated histoplasmosis (PDH) is associated with high mortality in people with advanced HIV disease or severe immunosuppression. The World Health Organization (WHO) recommends antigen (Ag) testing for PDH diagnosis. Objective. To assess the positivity of the Histoplasma Ag test in urine specimens referred to SYNLAB.
Materials and methods. A retrospective analysis of SYNLAB's database included specimens refereed from February 2021 to August 2023. Specimens were tested using the Clarus Histoplasma GM enzyme immunoassay (HGM) (IMMY).
Results. A total of 2,442 urine were tested, 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 Ag concentration was 9.25 EIA Units, significantly higher in adult patients (9.6 EIA Units) than 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, here we found that one in four patients tested positive. Higher positivity and Ag concentration were observed in adults. These findings highlight the importance of Ag testing in diagnosing PDH, particularly in high-risk populations.