There is still a normal urobilinogen stix result even though there is decreased to zero amounts of urobilinogen in the urine, due to the bile duct obstruction, because you CANNOT get a negative urobilinogen reading on the Multistix!  Look at the reagent strip below, notice that the first pad for urobilinogen constitutes a normal reading at 0.2 mg/dl; therefore, you cannot detect less than that, even if there is less than 0.2 mg/dl of urobilinogen in the urine.