Dark-field Exam

Aka: Dark-field Exam, Dark-field Microscopy, Syphilis Microscopy

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II. Indications

  1. Syphilis evaluation

III. Efficacy

  1. Most specific if Chancre or condyloma is present
  2. Accuracy varies with experience of technician

IV. Equipment Needed

  1. Microscope with dark-field condenser or
  2. Phase contrast microscope

V. Technique

  1. 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
  2. Place drop of sample onto glass slide; add cover slip
  3. Examine under dark-field or phase contrast microscope
    1. Single motile organism (corkscrew appearance)

VI. Interpretation: Positive Test

  1. Primary Syphilis Chancre
  2. Secondary Syphilis Condyloma Lata

VII. 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

VIII. References

  1. Larsen (1995) Clin Microbiol Rev 8:1-21 [PubMed]

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Ontology: Dark field examination (C1441544)

Concepts Laboratory Procedure (T059)
CPT 87166
LNC LP6219-2
English Dark field examination, dark field examination, dark field examination (procedure)
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Dark Field Microscopy (C2827982)

Definition (NCI_CDISC) A microscopic technique in which the light that does not come into contact with the structure or details of interest is subtracted from the ocular image. This yields an image in which the structure or details are alight while the areas where the structures or details are absent are dark.
Definition (NCI) A light microscopic technique in which the light that does not come into contact with the structures or details of interest is subtracted from the ocular image. This yields an image in which the structures or details are alight while the areas where the structures or details are absent are dark.
Concepts Laboratory Procedure (T059)
English Dark Field Microscopy, DARK FIELD MICROSCOPY
Derived from the NIH UMLS (Unified Medical Language System)

Related Topics in Pathology and Laboratory Medicine

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