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NBME 20 Answers

nbme20/Block 2/Question#13

A 25-year-old woman comes to the physician because ...

A phospholipid (cardiolipin) on charcoal particles

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Any answer with treponemes is used to syphilus only and is very specific. That only leaves cardiolipin, which is also elevated in SLE; this is why its sensitive but not specific in Syph.

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submitted by hayayah(603),

Diagnosis of Syph: Visualized by immunofluorescence or dark-field microscopy; serology is important – two types of antibodies:

  • Ab binds to cardiolipin: an antigen found in mammalian mitochondrial membranes and in treponemes; a cheap source of antigen is cow heart, which is used in screening tests; very sensitive in primary, except early, and secondary syphilis – titer may decline in tertiary and with treatment; but not specific – must confirm with FTA-ABS.
  • Examples include Venereal Disease Research Lab (VDRL), Rapid plasma Reagin (RPR), Automated Reagin Test (ART), or Recombinant Antigen Test (ICE)

  • Specific tests for treponemal antibody are more expensive; earliest antibodies bind to spirochetes: these tests are more specific and positive earlier; usually remain positive for life, but positive n patients with other treponemal diseases and may be positive in Mono, RF, Lupus, Leprosy, Lime, and Drug users.

  • The most widely used is Fluorescent Treponemal Antibody- Absorption (FTA-ABS) or Treponema pallidum microhemagglutination (MHA-TP)

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submitted by xxabi(145),

Non-treponemal tests are sensitive, but not specific - RPR, VRDL