HiE: How do current European guidelines – for example from ESCMID or ECMM – recommend the use of β-glucan (BDG) testing in the diagnosis of invasive fungal infections (IFI)? Dr. Frédéric Gabriel: ‘BDG testing is mostly recommended in two clinical situations: the diagnosis of invasive candidiasis (IC) and Pneumocystis pneumonia (PCP). According to the ECIL (European Conference on Infections in Leukaemia), BDG may be used in the diagnosis of PCP if Pneumocystis PCR on bronchoalveolar lavage (BAL) is not feasible.1 Similarly, BDG is one of the microbiological criteria for defining PCP according to the EORTC/MSGERC (European Organisation for Research and Treatment of Cancer / Mycoses Study Group Education and Research Consortium), provided that factors leading to false-positive BDG results and the presence of another IFI have been ruled out.2 The test is not indicated for monitoring PCP, as BDG may remain positive long after clinical resolution of the infection. ‘In the recent guidelines on the diagnosis of invasive candidiasis issued by the ECMM (European Confederation of Medical Mycology), in collaboration with ISHAM (International Society for Human and Animal Mycology) and the ASM (American Society for Microbiology), it is strongly recommended that BDG should only be used for IC in conjunction with clinical parameters, other biomarkers or other diagnostic tools.3 In the context of other IFI, and invasive aspergillosis in particular, BDG is no longer included in the 2019 EORTC/MSGERC criteria, as it offers no advantage over galactomannan testing.4 However, as noted by the British Society for Medical Mycology in its latest guidelines on best practice for the diagnosis of serious fungal diseases, BDG may sometimes still be useful for diagnosis.