AIIMS PG Entrance May 2015 – MCQ 33 – Three swab test

Dye found in the top swab in a three swab test is indicative of?
A. Uretero-vaginal fistula
B. Vesico-vaginal fistula
C. Urethro-vaginal fistula
D. Rectovaginal fistula

Correct answer : A. Ureterovaginal fistula

Obstetric fistula locationsCommon locations of obstetric fistula

Three swab test

  • Three swab test is used to differentiate between ureterovaginal fistula, vesicovaginal fistula and urethrovaginal fistula.
  • Three cotton swabs are placed in the vagina – at the vault, in the middle and just above the introitus.
  • Methylene blue is introduced into the bladder using a rubber catheter.
  • The patient is then asked to walk about for 5 minutes.
  • The swabs are then retrieved for inspection.

Interpretation of three swab test

  • Top swab soaked in urine, unstained – Uretero-vaginal fistula
  • Middle swab stained with dye – Vesico-vaginal fistula
  • Bottom swab stained with dye – Urethro-vaginal fistula

Image credits: Author: VHenryArt. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

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