Contribution of new diagnostic approaches to antifungal treatment plans in high-risk haematology patients

In high-risk patient cohorts, such as patients after solid-organ or allogeneic stem-cell transplantation, or patients with acute leukaemia, early diagnosis of invasive fungal infections (IFIs) is essential, as delayed or missing diagnosis of IFI results in increasing rates of mortality. However, diagnosis of most IFIs, especially of invasive aspergillosis, is difficult because classic tests have low sensitivity and specificity, and radiology often provides non-specific and transient results. The limited sensitivity and specificity of conventional assays for the detection of IFI and the growing number of immunocompromised patients who are at risk for opportunistic fungal infections have led to the development of new assays. These methods include antigen detection systems, such as ELISAs, and different molecular methods (PCR assays). Serological tests, such as the detection of the carbohydrate galactomannan, are standardised and commercially available. However, they still need to be evaluated in large patient cohorts, especially children. The benefit of antibody detection remains unclear if patients are under immune suppression or are heavily colonised but not infected. A range of different PCR assays (conventional, nested, real-time) have been developed, targeting different gene regions (cytochrome P450, heat-shock proteins, 18S, 5.8S, 28S, internal transcribed spacer), including a variety of amplicon detection methods, such as gel electrophoresis, hybridisation with specific probes, ELISA and restriction fragment length polymorphism. These molecular assays provide high potential in terms of sensitivity and specificity, but vary widely in their feasibility and up to now have not been standardised. Taken together, new non-culture-based diagnostic assays are appropriate as simple and rapid screening tests with high sensitivities and quick turnaround times. Thus, they might help to reduce empirical antifungal therapy and might be valuable tools to allow early initiation and monitoring of pre-emptive antifungal therapy. In this review, we assess the performance of a variety of non-culture-based tests for the detection of IFI in high-risk haematological patients, with emphasis on the impact of the assays on different management strategies.