Harring, Julie A

The detection of antibodies against Histoplasma capsulatum remains a frequently relied-on approach to diagnose histoplasmosis. We retrospectively assessed the performances of complement fixation (CF) and immunodiffusion (ID) assays for anti- Histoplasma antibody detection in patients with culture-confirmed histoplasmosis at Mayo Clinic (Rochester, MN) over a 10-year period (2011 to 2020).

ABSTRACT Detection of the Histoplasma capsulatum urinary antigen (UAg) is among the most sensitive and rapid means to diagnose histoplasmosis. Previously, we evaluated analyte-specific reagents (ASR) manufactured by IMMY (Norman, OK) for detection of Histoplasma galactomannan (GM) in urine using an enzyme immunoassay (EIA), and we showed low positive agreement (64.5%) with the MiraVista (MVista) Histoplasma antigen (Ag) quantitative EIA (MiraVista Diagnostics, Indianapolis, IN). Here we reevaluated the IMMY GM ASR following modification of our original assay protocol and introduction of an indeterminate range. A total of 150 prospectively collected urine samples were tested with both the IMMY and MVista EIAs, and clinical histories were recorded for all study subjects. The IMMY GM ASR showed positive and negative agreements of 82.3% (14/17 samples) and 100% (121/121 samples), respectively (with exclusion of 12 indeterminate results), and overall agreement of 90% (135/150 samples) with respect to the MVista EIA. Of the three patients with negative IMMY GM ASR results and positive MVista EIA results, testing was performed for initial diagnostic purposes for one patient (<0.4 ng/ml by the MVista EIA) and UAg levels were being monitored for the remaining two patients (both <0.7 ng/ml by the MVista EIA). The MVista EIA results were positive for 6/12 samples that tested indeterminate by the IMMY GM ASR. We also show that the IMMY GM ASR can be used to serially monitor Histoplasma UAg levels. In conclusion, we demonstrate that, with modification, the IMMY GM ASR is a reliable rapid assay for detection of Histoplasma UAg.