P392 Comparative evaluation of Wako β-glucan test and Fungitell assay for the diagnosis of invasive fungal infections
Authors: Singh Shreya , Agnihotri Sourav , Kaur Harsimran , Kanaujia Rimjhim , Ghosh Anup , Rudramurthy Shivaprakash 
Published: September 2022

Abstract

Poster session 3, September 23, 2022, 12:30 PM - 1:30 PM

Objectives
Serum 1,3 β-D-glucan (BDG) has shown wide utility as a broad fungal biomarker for invasive fungal disease (IFD). Fungitell assay (USA) is the only FDA-approved kit available for the detection of BDG. We planned to compare the performance of the Wako assay (Japan) with that of the Fungitell assay in patients with Invasive aspergillosis (IA) and invasive candidiasis (IC). We defined optimal cutoff values in the Wako assay to reliably exclude IFD (mainly due to Aspergillus and Candida).

Methods
A retrospective performance assessment study on archived patients’ serum samples, collected as part of routine clinical care at PGIMER, Chandigarh, India was performed. Only adult patients qualifying as proven/probable IFD as defined by EORTC/MSG criteria were included. Serum samples from patients with risk factors for IFD and not meeting the criteria for proven/probable disease (who had no evidence of IFD) were included as controls. A positivity threshold of 80 pg/ml was used for Fungitell assay. For the Wako, the optimum positivity threshold or cut-off was determined on subsequent analysis. We also noted the time to positivity for BDG test in the Wako assay.

Result
A total of 157 individuals, including 97 patients with IFD (33 IA and 64 IC) and 60 non-IFD controls were included in the study. Mean age of the participants was 40.8 ± 16.4 years and 63% were males. The mean BDG levels of Wako assay in various patient groups are depicted in Figure 1. A significantly higher BDG value was noted in patients with IFD vs. controls (70.79 vs. 3.03, P-value: .0002), IA vs. controls (112.3 vs. 3.034, P-value: &lt; .0001), and IC vs. controls (49.4 vs. 3.034, P-value: .0009). A good performance with an AUC of 0.990 for Fungitell and 0.895 for Wako assay was seen. The Youden's index on using the Wako assay at BDG cutoff of 11 pg/mL, 5 pg/ml, and 4 pg/ml were 0.598, 0.677, and 0.664 respectively. Based on this the cut-off of 5 pg/ml was selected as the optimum cutoff for the Wako BDG assay with a sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value and negative predictive value of 79.38%, 85%, 5.43, 0.22, 88.8%, and 73.9% respectively, for diagnosis of IFD. The percentage agreement between Wako and Fungitell assay was 84.7% with a Cohen's k score of 0.691. The mean time to positive test result (i.e., &gt; 5 pg/ml) was 37 min and the negative result was 87 min using the Wako assay compared with 120 min for the Fungitell test. However, an additional 15 min pre-treatment step was required in the Wako assay.

Conclusion
We observed that the performance of Wako assay is comparable to Fungitell assay. Results favored a lower cutoff value of 5 pg/ml compared with the kit specified cutoff of 11 pg/ml. Additionally, Wako assay gives positive results faster than Fungitell by allowing real-time observation. Further multi-centric studies on larger populations are required to establish the equivalence of these assays to guide clinicians in the diagnosis of IFDs.