Lab

Dark-field Exam

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Dark-field Exam, Dark-field Microscopy, Syphilis Microscopy

  • See Also
  1. Syphilis Serology
  2. Treponemal Specific Test
  3. Non-Treponemal Test
  4. Syphilis
  5. Neurosyphilis
  6. Sexually Transmitted Disease
  • Indications
  1. Syphilis evaluation
    1. Active stages of primary and Secondary Syphilis
  • Efficacy
  1. Most specific if a sample can be taken from an active Chancre or Condyloma Latum
  2. Accuracy varies with experience of technician
  • Technique
  1. Equipment Needed
    1. Microscope with dark-field condenser or
    2. Phase contrast microscope
  2. Obtain Sample
    1. Lymph Node saline aspirate
    2. Ulcerative lesion
      1. Clean lesion with saline
      2. Abrade lesion with gauze
      3. Do not use antiseptic
      4. Squeeze lesion to obtain drop of serous transudate
  3. Place drop of sample onto glass slide; add cover slip
  4. Examine under dark-field or phase contrast microscope
    1. Tiny helical organisms, moving in a corkscrew-like pattern
  • Interpretation
  • Positive Test
  1. Primary Syphilis Chancre
  2. Secondary Syphilis Condyloma Lata
  • Interpretation
  • Negative Test
  1. Does not rule out Syphilis
  2. At least 10^4 organisms must be present to be seen
  3. Repeat exam on three consecutive days
  • References
  1. Larsen (1995) Clin Microbiol Rev 8:1-21 [PubMed]