Dermatology Book

Fungal Infections

Viral Infection

Potassium HydroxideAka: KOH Preparation


  1. See Also
    1. Fungal Culture
  2. Collect specimen
    1. Skin
      1. Scrape scale with #15 blade or glass slide
    2. Vesicle
      1. Unroof Vesicle and examine roof material on slide
    3. Nail
      1. Scrape keratin debris with #15 or curette
    4. Hair
      1. Remove hairs gently with forceps or
      2. Scrape scale with glass slide or toothbrush
    5. Vaginal Discharge
      1. See Candida Vulvovaginitis
  3. Prepare with KOH
    1. Gather the scale into small mound and add KOH
    2. KOH Solution
      1. General
        1. Dissolves keratin but not hyphae walls
      2. KOH Preparations (5-20%)
        1. KOH alone
          1. Requires heating (See below)
        2. KOH with Dimethyl Sulfoxide (DMSO)
          1. Stable and does not require heating
        3. KOH with Swartz-Medrik Stain
          1. Keratin: Pink
          2. Hyphae: Blue
    3. Cover with coverslip
  4. Heating Technique
    1. Heat gently until bubbles begin to expand
    2. Heating is not required if KOH preserved with DMSO
  5. Examine
    1. Images
      1. DermLabKohHyphae.jpg
    2. Low Light and Low power (10x)
      1. Close condenser to its smallest opening
      2. Rack down slightly
      3. Locate piece of scale
        1. Look for branching structures (septate hyphae)
        2. Hyphae are on scale (NOT free floating)
        3. Differentiate from epithelial cell borders
          1. Overlapping cell borders may appear to branch
      4. Focus up and down to examine all levels of specimen
    3. Increase to high power (43x) to confirm yeast or hyphae
  6. Regulations: CLIA
    1. Provider-Performed Microscopy certificate required

KOH preparation (C1441630)

ConceptsLaboratory Procedure (T059)
EnglishKOH preparation
Derived from the NIH UMLS (Unified Medical Language System)

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