Accuracy of a novel histoplasmosis enzyme immunoassay to evaluate suspicious lung nodules

Background: Granulomas caused by infectious lung diseases present as indeterminate pulmonary nodules (IPNs) on radiography. Newly available serum enzyme immunoassay (EIA) for histoplasmosis has not been studied for the evaluation of IPNs. We investigated serum biomarkers of histoplasmosis antibodies as an indication of benign disease in IPNs from a highly endemic region. Methods: 152 serum samples from patients presenting with pulmonary nodules ≤30mm in maximum diameter were analyzed for histoplasmosis antibodies by immunodiffusion and EIA IgG and IgM tests. Serology and FDG-PET/CT scan diagnostic test characteristics were estimated and compared. Results: Cancer prevalence was 55% (n=83). Thirty-nine (26%) individuals were positive for IgG histoplasmosis antibodies. Twelve samples were IgM antibody positive. Immunodiffusion serology was similar to IgM antibody results with thirteen positive tests. Diagnostic likelihood ratios for benign disease were 0.62, 0.33 to 0.28 for FDG-PET/CT, IgG and IgM antibodies, respectively. When both IgG and IgM were positive (n=8), no nodules were cancerous and six were FDG-PET/CT avid. Conclusions: A positive EIA test for both IgM and IgG strongly suggested histoplasmosis etiology and benign granuloma for 12% of benign nodules arising from a highly endemic region. Presence of either IgG or IgM histoplasma antibodies was associated with benign disease. The EIA test was more sensitive in assessing histoplasma exposure than immunodiffusion serology. Impact: A new CLIA-certified histoplasmosis antibody EIA test measures histoplasmosis exposure, offers a possible alternative clinical diagnosis for benign IPNs and may improve IPN evaluation while avoiding harmful invasive biopsies.