Dermatologists and patients would be interested to know that the Chicago blue-KOH stain can be extremely useful for rapid diagnosis of fungal skin and nail infections. This is a simple bedside procedure where Chicago sky blue 6B (1%) is mixed with an equal volume of 10% KOH in a glass dropper bottle. A drop of this solution was then placed onto a microscope slide, onto which a sample of skin or nail was placed. A coverslip was applied over the sample and pressed to remove air bubbles. It was left to sit at room temperature for approximately 20 minutes and then examined for fungal elements at ×10 and ×40 magnifications using a light microscope.

See the picture below to see how fungi look like, with this stain. Pretty??

A comparison of the contrast stains, Chicago blue, chlorazole black, and Parker ink, for the rapid diagnosis of skin and nail infections

Background? The cheapest, most rapid method for the diagnosis of mycotic skin and nail infections is direct examination of samples using a KOH preparation. The standard KOH wet mount lacks a color contrast. Various contrast dyes are available. Parker ink is one which has been extensively used, however in recent times the stain no longer provides a suitable color contrast. Two other dyes that are available are Chicago blue and chlorazole black.

Methods? 100 samples of skin or nails were prospectively examined using Chicago blue, chlorazole black, and Parker ink-KOH stains. The samples were also cultured, with culture being the diagnostic gold standard.

Results? The sensitivities and specificities of the Chicago blue, chlorazole black and Parker ink stains were 78% & 96%; 63% & 97%; and 48% and 96%, respectively.

Conclusion? The Chicago blue-KOH stain provides a good color contrast and is a suitable replacement for the Parker ink-KOH stain. It is suitable for use in the dermatologist’s office or in the laboratory.

Article first published online: 12 JUL 2012

DOI: 10.1111/j.1365-4632.2011.05222.x

© 2012 The International Society of Dermatology

Issue

International Journal of Dermatology

Volume 51, Issue 8, pages 935–938, August 2012