Test performance of a commercial cryptococcal antigen lateral flow assay: a retrospective and prospective study at five Canadian sites

Cryptococcal antigen (CrAg) lateral flow assay (LFA) enables the rapid and sensitive detection of cryptococcal infection. The FungiXpert CrAg LFA is a Health Canada-licensed product that currently lacks evaluation in the North American setting. This retrospective and prospective study across five Canadian laboratories aimed to evaluate the FungiXpert CrAg LFA compared to the IMMY CrAg LFA for serum and cerebrospinal fluid (CSF) samples. Positive percent agreement (PPA) and negative percent agreement (NPA), precision, and cross-reactivity were assessed. A retrospective data review was performed for demographics, clinical data, and additional diagnostic testing results. A total of 141 serum samples and 93 CSF samples from 192 individuals were included. In the overall retrospective cohort, the FungiXpert CrAg LFA demonstrated qualitative detection PPA of 90.2% (95% confidence interval [95% CI], 87.3%-93.1%), and NPA of 100% (95% CI, 97.7%-100%). By sample type, the CSF PPA was 93.9% (95% CI, 79.8%-99.3%), and the serum PPA was 90.7% (95% CI, 79.7%-96.9%). The prospective cohort consisted of 58 samples, including two serum samples that were positive; of these, one was a low titer (1:1) and missed by FungiXpert. Both assays showed cross-reactivity with Trichosporon asahii. Inter-assay precision evaluation highlighted substantial variability in the FungiXpert CrAg LFA serum testing. These findings suggest similar performance of the FungiXpert CrAg LFA on CSF samples, but lower sensitivity on serum samples and greater lot-to-lot variability compared to IMMY CrAg LFA that should be considered in clinical implementation decision-making. In this Canadian multicenter study, the FungiXpert CrAg LFA demonstrated similar performance on CSF samples but lower sensitivity on serum samples compared to the IMMY CrAg LFA.IMPORTANCEThis multicenter Canadian evaluation provides the first North American performance data for the Health Canada-licensed FungiXpert cryptococcal antigen lateral flow assay. While performance on cerebrospinal fluid was comparable to the reference IMMY assay, reduced sensitivity for low-titer serum samples and greater inter-assay variability highlight important considerations for clinical implementation and assay selection.