Yeast Susceptibility, Custom MIC, 2 Drug

This test determines susceptibility of a rapidly growing and non-fastidious yeast isolate to antifungal agents (to be selected at the time of ordering). This test is performed on pure yeast isolates including Candida and Cryptococcus to aid in patient management.

The susceptibility of a yeast isolate is measured by determining the minimum inhibitory concentration (MIC), which is the lowest drug concentration that prevents growth. An isolate can be categorized as susceptible, intermediate, susceptible-dose dependent, or resistant by comparing the MIC of an isolate to established clinical breakpoints [1]. MIC interpretations are based on recently published guidelines from the Clinical and Laboratory Standards Institute (CLSI). When a clinical breakpoint for an antifungal agent is not established by CLSI guidelines, only the MIC value is reported. For additional guidance, please review current CLSI documents related to antifungal susceptibility testing of yeasts.

Because treatment outcomes are influenced by many factors (eg, drug pharmacokinetics, pharmacodynamics, and interactions; the patient's immune response; disease severity), a "susceptible" or a "resistant" result does not ensure that a patient will or will not respond to a particular drug.

Invasive yeast infections, commonly caused by Candida and Cryptococcus, are associated with significant morbidity and mortality especially in immunocompromised individuals [2,3]. Species of these organisms have unique virulence and antifungal susceptibility. A particular species can be resistant to some antifungal agents and susceptible to others. Therefore, species identification and antifungal susceptibility testing can help guide treatment decisions for invasive infections [4]. Yeast susceptibility testing is useful when a yeast's identity does not reliably predict its susceptibility, particularly when the identified yeast belongs to a species known to resist common antifungal agents [1].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. CLSI. Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts. 4th ed. CLSI guideline M27. Clinical and Laboratory Standards Institute; 2017.
2. Invasive candidiasis statistics. Centers for Disease Control and Prevention. Updated August 24, 2021. Accessed February 7, 2022. https://www.cdc.gov/fungal/diseases/candidiasis/invasive/statistics.html
3. C. neoformans Infection Statistics. Centers for Disease Control and Prevention. Updated May 26, 2020. Accessed February 7, 2022. https://www.cdc.gov/fungal/diseases/cryptococcosis-neoformans/statistics.html
4. Pappas PG, et al. Clin Infect Dis. 2016;62(4):e1-e50.