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Health Dictionary

Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.

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Athlete's foot laboratory findings

Introduction

Overview

Overview

  • Athlete’s foot can usually be diagnosed by visual inspection of the skin, but where the diagnosis is in doubt direct microscopy of a potassium hydroxide preparation (known as a KOH test).[1]
  • A KOH preparation is performed on skin scrapings from the affected area.
  • The KOH preparation has an excellent positive predictive value, but occasionally false negative results may be obtained, especially if treatment with an anti-fungal medication has already begun.
Laboratory Findings

Laboratory Findings

Microscopy

  • Skin scrapings from affected areas of toes, web spaces, soles including scales can be taken.[2]
  • To diagnose vesicular tinea pedis, the entire roof of the bulla is removed and mounted for a high yield of fungus.
  • Scrapings are stained with KOH and viewed under a microscope.
  • Counterstains may be used to better visualize the fungus such as chorazol black which is specific for chitin.
  • Dimethyl sulfoxide may be used to dissolve keratin in the scrapings.

Biopsy

  • A biopsy of the affected skin (i.e. a sample of the living skin tissue) can be taken for histological examination.

Culture

Immunochromatography

  • Immunochromatography kits use a solution to extract dermatophyte antigens from a tissue sample and detect their reaction with monoclonal antibodies to these antigens.[4]
  • This method is effective for tinea unguium but not very effective for tinea pedis.
  • Samples that test positive with this method are re-examined using microscopy or culture methods to make a final diagnosis.
References

References

  1. ↑ del Palacio, Amalia. “Trends in the treatment of dermatophytosis” (PDF). Biology of Dermatophytes and other Keratinophilic Fungi: 148–158. Retrieved 2007-10-10. Unknown parameter |coauthors= ignored (help)
  2. ↑ Nenoff P, Krüger C, Schaller J, Ginter-Hanselmayer G, Schulte-Beerbühl R, Tietz HJ (2014). “Mycology – an update part 2: dermatomycoses: clinical picture and diagnostics”. J Dtsch Dermatol Ges. 12 (9): 749–77. doi:10.1111/ddg.12420. PMID 25176455.
  3. ↑ Gupta AK, Chaudhry M, Elewski B (2003). “Tinea corporis, tinea cruris, tinea nigra, and piedra”. Dermatol Clin. 21 (3): 395–400, v. doi:10.1016/s0733-8635(03)00031-7. PMID 12956194.
  4. ↑ Tsunemi Y (2017). “Dermatophyte Antigen Kit”. Med Mycol J. 58 (2): J51–J54. doi:10.3314/mmj.17.005. PMID 28566667.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sanjana Nethagani, M.B.B.S.[2]