Double dye test
Double dye test is useful for diagnosing vesicovaginal or ureterovaginal fistulae. For this test, the patient takes oral phenazopyridine (Pyridium) 200 mg TDS, and indigo carmine or methylene blue is filled into the empty urinary bladder via a urethral catheter. Pyridium turns urine orange in the kidneys, and methylene blue (or indigo carmine) turns urine blue in the bladder.