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