Fluorescent brightener 85 (FB85), a new stain for diagnosing onychomycosis?

Calcofluor white is used to visualise fungal hyphae under the microscope, but it may not offer a great deal of additional utility over KOH in cases of suspected onychomycosis. Fluorescent brightener 85, a dye used in the wood and textile industries, may be a valuable alternative.

Onychomycosis is commonly diagnosed using 10% KOH direct microscopy, but this method can give false negative results. The only fluorescent stain currently used clinically is calcofluor white (CFW), which is more sensitive for some superficial fungal infections but does not appear to diagnosis of onychomycosis.

A new study by Xueping Yue and colleagues in Beijing evaluates the use of a new fluorescent reagent, FB 85, in cases of suspected onychomycosis. Of 108 specimens, 88.9% were positive using 0.1% FB 85 whereas only 55.6% were positive using the 10% KOH method. Fungal structures remained clearly visible for a longer time compared with the KOH method.

While no commercial FB 85 is currently available, FB 85 is a cheap water-soluble reagent that is already used widely in the wood and textile industries. This method also had a reduced preparation and observation time.

Read the paper: Yue et al (2018) Evaluation of a new fluorescent reagent, fluorescent brightener 85, for the diagnosis of suspected onychomycosis compared with potassium hydroxide. Mycoses 61:279-82.

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