This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Methylene blue 3 swab test is done for urinary fistulae. Source of leakage if the lowermost swab gets stained: March 2010 
Select and explain. 
A. Ureter, B. Urinary bladder, C. Urethra, D. None of the above
C: Urethra
Answer: C: Urethra 
Explanation: Ans. C: Urethra Methylene blue 3 swab test is useful for diagnosing site of leakage. In this test, Catheter is introduced in to the bladder through the urethra. Vaginal cavity is packed with 3 sterile swabs 50-100 ml of dilute methylene blue dye is injected into the bladder through the catheter (methylene blue turns urine blue). If VVF is present, methylene blue will stain the uppermost swab. If lowermost swab gets stained, the leak is from the urethra If the swab do not take up the stain but gets wet, leak is from the ureter.