Antifungal Susceptibility Testing: A Primer for Clinicians

Abstract

Antifungal susceptibility testing is not as commonly performed as antibacterial susceptibility testing. The methodology for detecting antifungal resistance is newer and requires different testing supplies that may not be readily available in a clinical laboratory setting. Breakpoints for molds are lacking. Yeast breakpoints are available for most antifungals but are continually updated based on epidemiologic surveillance. Reliable and reproducible antifungal susceptibility testing methods, as well as more research on the role of susceptibility testing in patient care, are necessary in order to provide the clinician with information that can be translated into positive clinical outcomes at the bedside. There are nuances with current testing methods that, if unrecognized, could lead to misinterpretation of results and inappropriate antifungal selection. Clinicians who have an understanding of qualitative and quantitative methods, automated susceptibility testing systems, and other commercial tests can successfully engage this knowledge to improve antifungal use and patient outcomes. This primer describes the common antifungal susceptibility tests used in the clinical microbiology laboratory and reviews literature related to the impact of appropriate drug selection, timing, fungal resistance mechanisms, pharmacokinetics, and pharmacodynamics on clinical outcomes. Both conventional and modern testing methods are discussed.