P412 QuicGM Aspergillus Galactomannan Ag lateral flow assay as a practical aid to diagnose invasive Aspergillosis in high-risk hematology patients

Abstract

Poster session 3, September 23, 2022, 12:30 PM - 1:30 PMBackgroundEarly diagnosis of invasive aspergillosis (IA) is an important factor to improve survival, but it remains challenging. QuicGM Aspergillus Galactomannan Ag Lateral Flow Assay (LFA) is based on a fluorescence immunochromatography test using a monoclonal antibody to identify Aspergillus galactomannan antigen in serum and bronchoalveolar lavage fluid.MethodsIn this study, we analyzed the diagnostic performance of QuicGM in 120 serum samples of high-risk hematology patients [41 cases of proven (n = 4) and probable (n = 37) IA and 79 equally high-risk controls] and compared it to performance of the galactomannan (GM) [Platelia Aspergillus enzyme immunoassay (ELISA) (Bio-Rad, Marnes-la-Coquette, France)]. Probable cases defined by a positive Biorad GM in serum were also included in the cohort.ResultsUsing the same cut-off of 0.5, QuicGM was positive in 22 cases versus GM in 21 cases. However, QuicGM was false positive in 11 controls with GM only in 1 control. These false positive samples remained positive upon repeated testing with the QuicGM. The test results of QuicGM and GM correlated well with a Spearman's correlation coefficient of 0.80 (P <.001). McNemar test showed no significant difference between both tests (P = 1) and Cohen's kappa coefficient was 0.65 (CI 0.49-0.81), suggesting a substantial strength of agreement.QuicGM sensitivity (using 0.5 cutoff) was 54% versus 51% for GM. Specificity was 86% for QuicGM versus 99% for GM. Positive predictive value (PPV) was only 67% for QuicGM versus 95% for GM. Combining GM and QuicGM in serum increased sensitivity to 59%. Youden index of QuicGM in the cohort was 0.39. Using this cutoff, sensitivity was 66% and specificity was 80%. When using a higher cutoff of 0.6 for the QuicGM, specificity increased to 94% and PPV to 78%, at the cost of a decrease in sensitivity to 44%.DiscussionIncluding probable cases defined by a positive Biorad GM in serum could have led to a bias in favor of the GM.With the cutoff suggested by the company, there was a notable decrease in specificity and PPV for the QuicGM. The need to adjust this cut-off must be questioned. With the implementation of LFAs in the EORTC-MSGERG criteria, one usually strives for the same cutoff of 0.5, to assure a practical approach. However, we must remain thoughtful about slight differences in these tests. They all have their own IgG and IgM built. Caution is needed more in the setting of diagnosis than in screening.More knowledge must be obtained regarding how different hospital laboratories have implemented the LFAs.ConclusionDiagnostic performances of QuicGM and Biorad GM correlate well.Further research is necessary regarding the optimal cutoff index.