A 38-years old patient who had a total abdominal hysterectomy presents 2 months postop complaining of leakage of urine from the vagina. On examination, no fistula can be identified. Dilute methylene blue (100mL) is injected into the bladder through a Foley catheter and a tampon is placed in the vagina. The patient is asked to walk for about 15 minutes, after which the patient is found to be wet, but there is no blue stain anywhere on the tampon. Which of the following is true:-

Explanation

Methylene blue Swab Test-- A catheter is introduced into the bladder through the urethra, The vaginal cavity is packed with three sterile swabs, 50-100 mL of dilute methylene blue dye is injected into the bladder through the catheter. If there is a VVF present, the methylene blue dye stains the uppermost swab.If the lowermost swab gets stained, the leak is from the urethra--> urethrovaginal fistula Swabs do not take up the stain, but get wet with urine, the leak is from the ureter-->ureterovaginal fistula