All Notes

Direct Microscopy-KOH Smear: Introduction, Uses, and Keynotes

Introduction

Direct microscopic examination is one of the most rapid and inexpensive diagnostic methods for detecting fungal elements in clinical specimens. Potassium hydroxide (KOH) smear is a routine technique in mycology that helps visualize fungal structures such as hyphae, yeast cells, and sclerotic bodies directly from patient samples. It is widely used as a first-line screening test for suspected fungal infections before culture or molecular testing.

Uses of Direct Microscopy-KOH Smear

Fig. Melanized septate fungal hyphae in KOH mount of BAL sample
Fig. Yeast cells and budding yeasts in a KOH mount of Urine
Fig. Yeast cells, budding yeasts, and pseudohyphae in KOH mount of sputum, microscopic examination at a magnification of 1600X
Fig. Yeast cells and budding yeasts in KOH mount of urinary sediment microscopy at a magnification of 1600X
Fig. Septate acute-angled branching hyphae of Aspergillus in a KOH mount of sputum
fIG. Fungal elements in the KOH mount of the urine sample at a magnification of 1600X
Fig. Chlamydospores of Candida albicans and hyphae in KOH mount of sputum microscopy at a magnification of 1600X
Fig. Heavy load of fungal elements in KOH mount of sputum specimen (Mag. 1600X)
Fig. In a potassium hydroxide (KOH) skin scraping for chromoblastomycosis, a sclerotic body is a characteristic, dark-brown, thick-walled, round, and multicellular fungal cell that appears as a “medlar body” or “muriform cell,” as shown in this image.

Keynotes on Direct Microscopy-KOH Smear

  1. Principle: KOH clears keratin and cellular debris, making fungal elements more visible under the microscope.
  2. Concentrations: 10% KOH for skin/hair, 20–40% KOH for nails; heating can enhance clearing.
  3. Visualization: Lactophenol, cotton blue, calcofluor white, or Parker ink can be added for contrast.
  4. Advantages: Simple, inexpensive, rapid, and highly useful in low-resource settings.
  5. Limitations: Cannot identify species; sensitivity depends on fungal load and observer experience.
  6. Best Use: Serves as an initial diagnostic step for suspected fungal infections in dermatology, ophthalmology, pulmonology, and general medicine.

Further Readings

  1. https://www.medicalnewstoday.com/articles/322331
  2. https://www.youtube.com/watch?v=LUwNQI_0BWU&t=1
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8654087/
  4. https://flabslis.com/blogs/koh-test-procedure
  5. https://www.healthline.com/health/skin-lesion-koh-exam
  6. https://drkothiwalaskineva.com/medical-dermatology/koh-mount-for-fungal-diseases/
  7. https://pmc.ncbi.nlm.nih.gov/articles/PMC11642458/
  8. https://en.wikipedia.org/wiki/KOH_test
  9. https://journals.lww.com/ijpd/fulltext/2020/21040/mount_the_menace____potassium_hydroxide_in.26.aspx
  10. https://diag.vn/en/thongtinyte/koh-in-nail-and-skin-mycology-diagnosis/
  11. https://www.linkedin.com/posts/dip-ghosh-2329b3291_clinicalmycology-medicallaboratory-fungalinfections-activity-7359249932584722434-79Yj
  12. https://iacdworld.org/wp-content/uploads/2016/12/kohpreparation.pdf

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