Preliminary Development and Clinical Evaluation of a Locally Produced ELISA for Urinary Histoplasma Antigen Detection in Argentina

Background: Histoplasmosis is a major opportunistic fungal infection in immunocompromised individuals, particularly people living with HIV in Latin America. Early diagnosis is essential to reduce morbidity and mortality, but commercial urinary Histoplasma antigen assays are not consistently accessible in many endemic settings. Methods: We developed a locally produced enzyme-linked immunosorbent assay (ELISA) to detect urinary Histoplasma antigen in urine and performed a preliminary clinical evaluation. The assay is based on a sandwich ELISA format using rabbit polyclonal antibodies raised against whole-killed yeast cells of Histoplasma capsulatum. Receiver operating characteristic (ROC) analysis was performed with urine samples from patients with progressive disseminated histoplasmosis (PDH) (n = 37) and healthy controls (n = 20). An exploratory disease-control panel (n = 11) was also tested to assess cross-reactivity. Preliminary analytical characterization included blank-based estimation of the limit of detection (LOD) and limit of quantification (LOQ). Results: Using a Youden-derived cutoff of OD492 = 0.243, the in-house ELISA showed a sensitivity of 73.0% (27/37; 95% CI: 55.9–86.2%) and a specificity of 100.0% (20/20; 95% CI: 83.2–100.0%) in the main ROC dataset, with an area under the curve of 0.856. In the exploratory disease-control panel, 2 of 11 specimens were reactive (one paracoccidioidomycosis and one cryptococcosis sample). Preliminary LOD and LOQ estimates were 4.46 ng/mL and 8.15 ng/mL, respectively. Conclusions: This locally developed ELISA represents a feasible and cost-effective alternative for urinary antigen detection of Histoplasma, with potential to improve access to early diagnosis in resource-limited settings. However, its current performance should be considered preliminary. Additional optimization and broader validation, including direct comparison with commercial assays, inter-assay precision, reagent stability, and larger multicenter control panels, are required before routine clinical implementation.